Occam's Razor

[Dr B]

This is often totally misquoted by many people, misapplied by others and ill-understood.

What I am interested in here is asking people what they understand the Razor to mean. In addition, does anyone have a reliable early source for the proper statement of the Razor (and can provide the reference)?

Most of the time I see the public use it - i see it mis-quoted or mis-applied - which leads to confusion.

[Melanie]

(Pretty definitive, I think...)

Occam's (or Ockham's) razor is a principle attributed to the 14th century logician and Franciscan friar; William of Occam. Ockham was the village in the English county of Surrey where he was born.

The principle states that "Entities should not be multiplied unnecessarily." Sometimes it is quoted in one of its original Latin forms to give it an air of authenticity.

"Pluralitas non est ponenda sine neccesitate"
"Frustra fit per plura quod potest fieri per pauciora"
"Entia non sunt multiplicanda praeter necessitatem"

In fact, only the first two of these forms appear in his surviving works and the third was written by a later scholar. William used the principle to justify many conclusions including the statement that "God's existence cannot be deduced by reason alone." That one didn't make him very popular with the Pope.

Many scientists have adopted or reinvented Occam's Razor as in Leibniz's "identity of observables" and Isaac Newton stated the rule: "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances."

The most useful statement of the principle for scientists is,

"when you have two competing theories which make exactly the same predictions, the one that is simpler is the better."

In physics we use the razor to cut away metaphysical concepts. The canonical example is Einstein's theory of special relativity compared with Lorentz's theory that ruler's contract and clocks slow down when in motion through the Ether. Einstein's equations for transforming space-time are the same as Lorentz's equations for transforming rulers and clocks, but Einstein and Poincaré recognised that the Ether could not be detected according to the equations of Lorentz and Maxwell. By Occam's razor it had to be eliminated.

The principle has also been used to justify uncertainty in quantum mechanics. Heisenberg deduced his uncertainty principle from the quantum nature of light and the effect of measurement.

Stephen Hawking explains in A Brief History of Time:
"We could still imagine that there is a set of laws that determines events completely for some supernatural being, who could observe the present state of the universe without disturbing it. However, such models of the universe are not of much interest to us mortals. It seems better to employ the principle known as Occam's razor and cut out all the features of the theory that cannot be observed."

But uncertainty and the non-existence of the ether cannot be deduced from Occam's Razor alone. It can separate two theories that make the same predictions, but does not rule out other theories that might make a different prediction. Empirical evidence is also required and Occam himself argued for empiricism, not against it.

Ernst Mach advocated a version of Occam's razor which he called the Principle of Economy, stating that "Scientists must use the simplest means of arriving at their results and exclude everything not perceived by the senses." Taken to its logical conclusion this philosophy becomes positivism; the belief that there is no difference between something that exists but is not observable and something that doesn't exist at all. Mach influenced Einstein when he argued that space and time are not absolute but he also applied positivism to molecules. Mach and his followers claimed that molecules were metaphysical because they were too small to detect directly. This was despite the success the molecular theory had in explaining chemical reactions and thermodynamics. It is ironic that while applying the principle of economy to throw out the concept of the ether and an absolute rest frame, Einstein published almost simultaneously a paper on brownian motion which confirmed the reality of molecules and thus dealt a blow against the use of positivism. The moral of this story is that Occam's razor should not be wielded blindly. As Einstein put it in his Autobiographical notes:

"This is an interesting example of the fact that even scholars of audacious spirit and fine instinct can be obstructed in the interpretation of facts by philosophical prejudices."

Occam's razor is often cited in stronger forms than Occam intended, as in the following statements. . .

"If you have two theories which both explain the observed facts then you should use the simplest until more evidence comes along"

"The simplest explanation for some phenomenon is more likely to be accurate than more complicated explanations."

"If you have two equally likely solutions to a problem, pick the simplest."

"The explanation requiring the fewest assumptions is most likely to be correct."

. . .or in the only form that takes its own advice. . .
"Keep things simple!"

Notice how the principle has strengthened in these forms which should be more correctly called the law of parsimony, or the rule of simplicity. To begin with, we used Occam's razor to separate theories that would predict the same result for all experiments. Now we are trying to choose between theories that make different predictions. This is not what Occam intended. Should we not test those predictions instead? Obviously we should eventually, but suppose we are at an early stage and are not yet ready to do the experiments. We are just looking for guidance in developing a theory.

This principle goes back at least as far as Aristotle who wrote "Nature operates in the shortest way possible." Aristotle went too far in believing that experiment and observation were unnecessary. The principle of simplicity works as a heuristic rule-of-thumb but some people quote it as if it is an axiom of physics. It is not. It can work well in philosophy or particle physics, but less often so in cosmology or psychology, where things usually turn out to be more complicated than you ever expected. Perhaps a quote from Shakespeare would be more appropriate than Occam's razor: "There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.".

Simplicity is subjective and the universe does not always have the same ideas about simplicity as we do. Successful theorists often speak of symmetry and beauty as well as simplicity. In 1939 Paul Dirac wrote,


"The research worker, in his effort to express the fundamental laws of Nature in mathematical form should strive mainly for mathematical beauty. It often happens that the requirements of simplicity and beauty are the same, but where they clash the latter must take precedence."

The law of parsimony is no substitute for insight, logic and the scientific method. It should never be relied upon to make or defend a conclusion. As arbiters of correctness only logical consistency and empirical evidence are absolute. Dirac was very successful with his method. He constructed the relativistic field equation for the electron and used it to predict the positron. But he was not suggesting that physics should be based on mathematical beauty alone. He fully appreciated the need for experimental verification.

The final word is of unknown origin, although it's often attributed to Einstein, himself a master of the quotable one liner:

"Everything should be made as simple as possible, but not simpler."

The pithiness of this quote disguises the fact that no one knows whether Einstein said it or not (this version comes from the Reader's Digest, 1977 [US: July, UK: October?). It may well be a precis of the last few pages of his "The Meaning of Relativity" (5th edition), where he wrote about his unified field theory, saying "In my opinion the theory here is the logically simplest relativistic field theory that is at all possible. But this does not mean that nature might not obey a more complex theory. More complex theories have frequently been proposed. . . In my view, such more complicated systems and their combinations should be considered only if there exist physical-empirical reasons to do so."

References:

W. M. Thorburn, "Occam's razor", Mind, 24, pp. 287-288, 1915.

W. M. Thorburn, "The Myth of Occam's razor", Mind, 27, pp. 345-353, 1918.

Stephen Hawking, A Brief History of Time.

Albert Einstein, Autobiographical notes

Isaac Newton, Principia: The System of the World

[Melanie]

It's usually interpreted simply to mean 'where there are several theories the simplest is probably the correct one'.

Unfortunately, this is not necessarily what Occam meant.

Particularly in paranormal investigations, it's sometimes used without much thought when people are trying to reach a conclusion about the cause of, say, a haunting. If 'stuff' happens, then there may be several ideas about the cause of said 'stuff'. Some of these may be very complicated, for example, EMF affecting the human brain. If there's an existing ghost legend attached to the place, it's 'simpler' to say it's the Ghost that's causing the effects.

(Of course, the physics behind the ghost's very existence and it's interaction with the environment is seldom explained, and that could get very complicated!)

[Mojo]

The principle states that "Entities should not be multiplied unnecessarily."

Or in plain English, "don't make stuff up".

[wollery]

The principle states that "Entities should not be multiplied unnecessarily."

Or in plain English, "don't make stuff up".
Or more accurately, "don't make stuff up unnecessarily".

[Lord Muck oGentry]

I've always liked the second formulation Melanie quotes. A reasonable translation would be: what is done with more that can be done with less is done pointlessly. A premiss that can be dropped without affecting the conclusion plays no part in the explanation.

[Dr B]

So, what would people here think to the idea that Occams razor can only be applied to empirical arguments?

It seems - based on the history outlined above it has been applied to all forms of argument (though not necessarily with equal effect). Are there times when you think the razor cannot be applied?

[Cuddles]

The razor can always be applied, but it is not always right. As an anology with Murphy's law, things are not always guaranteed to go wrong, but you are best off assuming they will. Same with Occam, the simplest explanation is not always the right one, but you are generally best off assuming it is until you have a good reason to think otherwise.

[Dr B]

Sounds good to me.....I am thinking of writing a paper for my students on the mis-applications and misquotations of the razor. Also how pseudoscientists try to use it to fudge their ideas.

Many thanks everyone - if there are anymore suggestions let me know and I will give it some thought.

[Lord Muck oGentry]

Sounds good to me.....I am thinking of writing a paper for my students on the mis-applications and misquotations of the razor. Also how pseudoscientists try to use it to fudge their ideas.

Many thanks everyone - if there are anymore suggestions let me know and I will give it some thought.

Rather late, I know, but here it is anyway:

http://www.logictutorial.com/occam.html

I must have bookmarked this an age ago and then forgotten to post it.

[Lord Muck oGentry]

Simple reductio argument to show why redundant premisses are bad news.

Let p, q and r be premisses, each logically independent of the others, that constitute a theory, and s the predicted outcome.

Let the evidence for a theory be whatever the theory correctly predicts*.

Let
1. (p.q)>s ( parsimonious explanation, shunning r)

2. (p.q.r)>s ( trivially, from 1 and assumptions above)

3. (p.q.~r)>s ( as for 2 )

Wherever s is true, it is evidence for both 2 and 3, and therefore for both r and ~r. Any redundant premiss can be cheaply evidenced. Unfortunately, so can its denial.





*Gross over-simplification, I know. But the difference won't help the redundancy fancy.

[dalriada]

I came across a lovely occam type quotation yesterday. I spent the day in Queens University library indulging in some spookifying with some notebooks written by Edith Somerville (1858-1948 ), author of "The Irish RM" books. The notebooks contain details of her psychic interests and seance records-she had a life-long interest in the paranormal and some strong family connections with the early days of the Society for Psychical Research (her uncle was vice-president at one stage). Anyway the following passage made me laugh out loud, because even today, it's still so true :


"There is a class of investigator (in psychic things) who loves to wander around in circles. He trips continually over his own brains and can never persuade himself that the simple and obvious explanation is also the true one. His intellect becomes a positive curse to him for he uses it to avoid the straight road and fashion out some strange devious path which lands him at last in a quagmire"

Just beside that in the margin there's a name, "Conan Doyle", who was her distant relative. I wonder if that remark was something he said, or if it was her own personal opinion about him...?

[Mongrel]

Excellent quote dalriada, that's going in my sig file ;)

"He trips continually over his own brains", just wondering if this is what happens when you walk around with an "open" mind all day :smiley:

[Mulder]

Occam's Razor is just for people who can't be bothered to get enough evidence! They deserve to live in a universe of guesswork.

[bobdezon]

That is not the purpose of occhams razor as Dr B already illustrated. It is a philosphical cognative concept with real world applications.

[Mulder]

Sometimes the real answer isn't the simplest. To tell if that's the case you need more evidence. Until then you are just speculating.

[Cuddles]

Which just proves that you haven't actually understood any of this thread. To start with, Occam's Razor doesn't actually say anything about simplicity.

[Mulder]

I'm sure you're right though I did see the words 'simple', 'simplest', 'simply' used by various people. I guess it was all the other words I didn't understand. Mea culpa.

[Janot]

"when you have two competing theories which make exactly the same predictions, the one that is simpler is the better."

This is what it boils down to - not necessarily simple - the comparative is the key

[Mongrel]

Wiki has it as (http://en.wikipedia.org/wiki/Occams_razor)
"entia non sunt multiplicanda praeter necessitatem", or "entities should not be multiplied beyond necessity. This is often paraphrased as "All other things being equal, the simplest solution is the best." In other words, when multiple competing theories are equal in other respects, the principle recommends selecting the theory that introduces the fewest assumptions and postulates the fewest entities. It is in this sense that Occam's razor is usually understood."

Simple example; Crop Circles - Aliens from another planet with a message or a hoax started by drunk students?

We have no conclusive proof of extraterrestrials and can think of no good reason why they'd leave bizzare symbology in the middle of fields after travelling vast distances.

Students on the other hand - we know they exist, we know they're often up for a laugh and that most of them include beer in their nutritional calculations

Which one of these theories has the least assumptions?

[Mulder]

Wiki has it as (http://en.wikipedia.org/wiki/Occams_razor)

Simple example; Crop Circles - Aliens from another planet with a message or a hoax started by drunk students?

We have no conclusive proof of extraterrestrials and can think of no good reason why they'd leave bizzare symbology in the middle of fields after travelling vast distances.

Students on the other hand - we know they exist, we know they're often up for a laugh and that most of them include beer in their nutritional calculations

Which one of these theories has the least assumptions?

Just my point - you have evidence that students exist but not ET. So, you didn't need Occam's Razor at all.

OK, OK, I know you're going to tell me I've got it all wrong again, so please tell me this: why is Occam's Razor valid? What is the philosophical or scientific reasoning behind it? Better keep it simple for me, though ...

[Cuddles]

Just my point - you have evidence that students exist but not ET. So, you didn't need Occam's Razor at all.

That is Occam's razor.

[Mulder]

OK, but on the evidence so far presented here, it still COULD be aliens! You haven't eliminated that possibility, merely dismissed it through an assumption. What philosophical or scientific reason is there that it should be true? Without further evidence you are still just speculating.

[bobdezon]

If there was no evidence of aliens why would you assume it was aliens? ???

[Mulder]

You're applying the razor there, which is what I'm questioning. I'm saying, until you have sufficient evidence that it IS students, you can't just ASSUME that it ISN'T aliens. If aliens do exist, they might consider it amusing to put messages we might understand in crops. It's unlikely we could understand their mentality as they'd probably be a lot different to us. So we can't say how likely it is that they would mess around producing crop circles.

My point is, don't waste time speculating or assuming when you can't eliminate alternative possible theories. Instead, go out and find the evidence to decide between theories. Take the Bayesian approach if you like but, until you get the evidence, don't assume anything.

[bobdezon]

You're applying the razor there, which is what I'm questioning. I'm saying, until you have sufficient evidence that it IS students, you can't just ASSUME that it ISN'T aliens.

Using that logic, why isnt it also possible to assume it was a herd of clowns or kamikaze pigeon attack?


If aliens do exist, they might consider it amusing to put messages we might understand in crops. It's unlikely we could understand their mentality as they'd probably be a lot different to us. So we can't say how likely it is that they would mess around producing crop circles.

If as you insist we cannot fathom alien motives, then it is totally pointless speculating about such motives as we are unlikely to even be remotely correct. This is an assumption too far.


My point is, don't waste time speculating or assuming when you can't eliminate alternative possible theories. Instead, go out and find the evidence to decide between theories. Take the Bayesian approach if you like but, until you get the evidence, don't assume anything.

Baybesian is still a statistical probability factor like occhams razor. There is no evidence for aliens why must their "possible influence" be taken into account? That makes no sense. You are creating a factor which has no relevance or bearing on the case at hand.

[ZERO]

You're applying the razor there, which is what I'm questioning. I'm saying, until you have sufficient evidence that it IS students, you can't just ASSUME that it ISN'T aliens. If aliens do exist, they might consider it amusing to put messages we might understand in crops. It's unlikely we could understand their mentality as they'd probably be a lot different to us. So we can't say how likely it is that they would mess around producing crop circles.

My point is, don't waste time speculating or assuming when you can't eliminate alternative possible theories.
But alternative mutiple theories, like aliens which you would include, are a waste of time. Where do you draw the line?

until you get the evidence, don't assume anything.
Exactly. Why assume aliens did it. A razor approach keeps a multitude of silly theories away.

[Mulder]

OK, let me keep this simple as we are starying from the point.

I can't see any scientific or philosophical justification for Occam's razor. Several people on here obviously can because they are defending it. So, can someone please explain, in simple terms (because clearly I "haven't actually understood any of this thread"), WHY the razor is justified? What is the evidence that, given two or more possible theories to explain a set of evidence, the one with least assumptions/simplest/whatever should always be chosen?

And why should we make any choice at all until there is sufficient evidence to discriminate between the theories?

[ZERO]

OK, let me keep this simple as we are starying from the point.

I can't see any scientific or philosophical justification for Occam's razor. Several people on here obviously can because they are defending it. So, can someone please explain, in simple terms (because clearly I "haven't actually understood any of this thread"), WHY the razor is justified? What is the evidence that, given two or more possible theories to explain a set of evidence, the one with least assumptions/simplest/whatever should always be chosen?
First, there is no guarantee the simpilest will be correct, but it will be the easiest to prove/disprove. Why burden yourself with overly complicated theories first, when the simpiler ones can be dismissed first? Also, the more variables, the more room for error.


And why should we make any choice at all until there is sufficient evidence to discriminate between the theories?
At what point do you consider you have enough evidence?
Perhaps scant evidence can lead to theories that in turn lead to more evidence.

[Mulder]

First, there is no guarantee the simpilest will be correct, ...

So you agree with me! Nice to know I'm not the only one skeptical of Occam's Razor here.


At what point do you consider you have enough evidence?
Perhaps scant evidence can lead to theories that in turn lead to more evidence.

I agree. A theory should provide predictions for you to test which will differentiate it from all those other theories that you haven't dismissed a priori using the Razor.

PS: You used the forbidden 'S' word! Remember 'To start with, Occam's Razor doesn't actually say anything about simplicity.'

[ZERO]

PS: You used the forbidden 'S' word! Remember 'To start with, Occam's Razor doesn't actually say anything about simplicity.'

It is implied. Anyway I'm a rebel.

As I understand it. If you have two or more competing theories that reach the same conclusion, Occam's Razor would have you pick the one with the least assumptions.
Remember, an assumption is not a fact.
That seems a very reasonable way of making progress.

I don't think anyone has said OR is infalible and will always pick the right theory.
I don't think anyone advocates discarding forever theories that OR removes. New evidence is always possible.

If you think about it, allowing unlimited assumptions is not a good thing.

[Dr B]

Confusion...confusion....confusion. This is exactly the type of confusion I was trying to highlight in the OP

OK - Occam's razor has nothing to do with simplicity per-se. Simplicity is a consequence of the razor.

It is a reasoning heuristic which helps with both deductive and inductive logic - but is particularly useful to the more inductive sciences.

The razor is about necessity not simplicity. If it is not necessary to assume something in an account or theory - then don't assume it - it is redundant and not needed - as such it can be 'cut out' of reasoning as it plays no part in it. Quite often - theories based only on necessary assumptions will be simpler (but not always - but as I said - its usually a consequence of the razor)

What people have to do is make a case (i.e., a reasoned case based on evidential reasoning etc) to include all premises in their accounts. If this can be done, and stand the test of scientific scrutiny, then fine - the premise is justified and necessary - if not - then remove it and see how the account stands now. If it stands equally well (or even better) - then there is no need for multiplicative premises.

You can assume the tooth fairy is real, or you can assume that your parents put the money under your pillow. Now, as a theoretical starting point - are both these assumptions equally warrented and are they both necessary to explain the 50 pence piece under your pillow? ???

[ZERO]

Confusion...confusion....confusion. This is exactly the type of confusion I was trying to highlight in the OP

OK - Occam's razor has nothing to do with simplicity per-se. Simplicity is a consequence of the razor.

It is a reasoning heuristic which helps with both deductive and inductive logic - but is particularly useful to the more inductive sciences.

The razor is about necessity not simplicity. If it is not necessary to assume something in an account or theory - then don't assume it - it is redundant and not needed - as such it can be 'cut out' of reasoning as it plays no part in it. Quite often - theories based only on necessary assumptions will be simpler (but not always - but as I said - its usually a consequence of the razor)

What people have to do is make a case (i.e., a reasoned case based on evidential reasoning etc) to include all premises in their accounts. If this can be done, and stand the test of scientific scrutiny, then fine - the premise is justified and necessary - if not - then remove it and see how the account stands now. If it stands equally well (or even better) - then there is no need for multiplicative premises.

You can assume the tooth fairy is real, or you can assume that your parents put the money under your pillow. Now, as a theoretical starting point - are both these assumptions equally warrented and are they both necessary to explain the 50 pence piece under your pillow? ???

If you asked me a week ago, I would of said I understood Occam's bloody Razor.

Observation/evidence: 50 pence under pillow.
Theory 1: Parents put it there. Parents exist, have proof.
Theory 2: Tooth fairy put it there. Assume Tooth fairy exists, have no proof.
Theory 3: Stranger put it there. Strangers exist, have proof.

Now OR would remove #2 because it has an assumption although it is neccessary for that theory. OR can not be used to choose between #1 and #3 without more data. OR still holds #2 valid because it has no unneccessary assumptions but decrees other theories better.

Is this sound reasoning?

[Dr B]

No not quite.

OR does not, in any way, support theory 2. There is no evidence for Theory 2 so OR cannot be applied to it in that way. You have to make a whole host of a-priori assumptions to make it work in the first place - OR would cut those out initially. In other words - the case for fairies is unecessary - so it does not compete as an account.

OR is best applied to scientific theories - in that all have some evidence in support of them.

Indeed, Occam himself came to argue that the razor should not be applied to belief systems (religions etc).

Although strangers do exist - them being in your house in the night is unlikely to be true - so OR only really lends support to your parents (or caregiver) putting it there.

I am cutting out a great deal of context here (which is important) - but this is the essence of it.

If I get more time later - I will pop back and post more - but I am very very busy at the moment O0

Hope this helps....

[Dr B]

OK I am going to include just a few sections of a paper I am writing on Occam's razor. I apologise for the length. Note - the sections here have been edited and do not constitute the full article. I provide it here purely for educational purposes for those still struggling with the concept. I really hope it helps. O0 parts of it are based on philosophical sources and scientific ones which are fully credited in the full article which will be made available to UKS when it is completed. I have omitted citations here - purely for reasons of clarity and to remain concise. Anyway, as OR is a principle, most sources say the same thing.......


Background
Over the years philosophers and scientists have developed a legion of principles for thinking about the world. These methods include the principles of logic, reason, argumentation, and the scientific method itself. One principle of reasoning commonly recruited in a variety of philosophical and scientific arguments is that of Occam’s razor (or Ockham’s razor as it is also known: see below) which is also more commonly referred to as the principle of parsimony.
Most people have heard something about Occam’s razor – but few seem to truly understand it. It is often referred to in science-based films and the popular media though it is rarely represented in its correct form. For example in the science fiction film ‘Contact’ (starring Jodie Foster) her co-star’s character asks if she is familiar with the principle of Occam’s razor – and then goes on to state it as the principle of the simplest idea always being the best one. This appears to be based in the notion that, when there are several competing theories, ‘the simplest is always most likely to be the correct one'. However, this sound-bite version of the principle is not entirely correct and was not what Occam actually proposed at all. Simple ideas can be quite wrong and relatively complicated ideas are more than capable of being correct. These instances go against a strict notion of the razor cast as a principle of simplicity alone. In contrast to popular opinion, at no point did Occam ever state that the simpler explanation is always more correct or that the more complex explanation is always less correct. The essence of the point, in its proper context, is to start from the simplest possible explanation and make it more complex only if, and when, absolutely necessary.
Like any technique or principle Occam’s razor can be applied incorrectly, and it will be less useful or relevant if applied under inappropriate circumstances. Here we explore briefly the concept of Occam’s razor, in its correct form, and its implications for scientific reasoning. It should be noted that a great deal of philosophical debate still surrounds the use and application of the razor to certain forms of knowledge – but this debate lies outside the scope of the current discussion (see Carroll, 2003; 2005; Hyman & Walsh, 1973 for more detailed discussions).


...............snip......

A bit of historyOccam's razor (or Ockham's razor as it was originally known) is a reasoning principle attributed to William of Ockham, a 14th century logician and Franciscan monk (ca. 1285-1349). Ockham did not invent the principle – his name became associated to the principle because he used it extensively in his philosophical reasoning. We can glean an important insight into the essence of the principle when we consider some of the Latin statements associated with the original form of the razor. These include; (i) Entia non sunt multiplicanda praeter necessitatem, (ii) Pluralitas non est ponenda sine necessitate, and (iii) Frustra fit per plura quod potest fieri per pauciora. A rough translation of the principle is that; “Entities should not be multiplied unnecessarily”. By the term ‘entities’ Occam was referring to theoretical constructs / premises and the assumptions required in reasoning. According to this principle, all valid, reasonable explanations should be based on observable, demonstrable facts, complemented by additional logic and reasoning.
The exact phrasing of the principle is not absolutely crucial. Indeed, we can rephrase the principle in a number of ways without loosing the essence of it. For example, we could state it as; “do not make unnecessary assumptions” or “do not add assumptions that are unnecessary for the theory / conclusion” or even, “if an assumption is not necessary for the explanation – don’t recruit it in the argument”. To put it another way, if we can remove the trimmings of unnecessary assumptions and premises without it impacting on the quality of the conclusion, then those trimmings are unlikely to play a part in the explanation. As a consequence – they should be dropped as they play no part in the reasoning and thus have no consequence for the conclusion. It follows that if a premise or reason cannot be justified, and hence, a case for its necessity in the argument cannot be made – then the assumption is not only unfounded – but it may also be totally unnecessary!

.............snip.............

Necessity, simplicity and justifiability
As noted above, Occam’s razor is a logical tool that is employed to cut out irrelevant, unnecessary aspects from scientific arguments and philosophical systems. The central aspect of the principle is necessity. If it is not absolutely necessary to introduce certain complexities or hypothetical constructs into a given explanation, then don’t do it. From this we can see that it is necessity and not simplicity that the principle depends on. However, these two factors are not mutually exclusive and they certainly enjoy some degree of interdependence. Any theory or argument which has applied the razor correctly (based on including only those premises and reasons which are necessary) is also likely to be simpler than rival explanations where the principle has not been applied. To put it another way, simplicity can be a consequence of necessity. Despite this close relationship – it is still more correct to view the principle in terms of necessity and not directly as simplicity per-se.
Having acknowledged the importance of necessity in the principle, the problem in some types of arguments is that it is not at all clear which reasons / evidence / premises / conclusions, are actually necessary. In other words, necessity itself is not always automatically known. In some areas of science like Physics and Mathematics the necessary assumptions may be more explicit and incontrovertible – particularly if the argument is based on mathematical constants and procedures. However, in sciences like Psychology and Neuroscience, which rely more on inductive forms of probabilistic reasoning, the ‘necessary’ assumptions are not always clear. In these circumstances one has to make the case through argument and theory. Here what one is really doing is justifying ones assumptions and showing why they are necessary. In any given argument, if you can justify why certain reasons must be considered when developing a theory for the object being studied, then you have made a case for it being necessary. As such, the concept of ‘justifiability’ is closely related to the principle of necessity in certain forms of inductive scientific reasoning and argumentation.

.....snip.....


The appropriate and inappropriate use of Occam’s razor
Many people, including scientists, do not seem to fully understand the principle of Occam’s razor or have used it inappropriately in their arguments. These instances are fallacious, and do not constitute sound, scientific arguments. For example, Pseudoscientists and creationists argue that the notion of a God creating the universe and the human species is simpler than the accounts proposed by Physics and Evolutionary biology (i.e., natural selection). As such, they claim that it is more in line with Occam’s razor than the scientific accounts. This is not true. We have already discussed that the principle is not directly about simplicity. In addition the concept of ‘God’ may itself be an unnecessary assumption. Furthermore, it is not clear at all how this assumption is simpler. This type of argument also reveals the limitations of how to use Occam’s razor appropriately in argumentation and theory.
Firstly, Occam’s razor should not be applied to metaphysical beliefs like those generated by religion and faith-based systems. This is mainly due to the lack of observable evidence from such knowledge systems on which the principle needs to rest. The principle is for separating scientific accounts, not for separating metaphysical and scientific accounts. Secondly, Occam’s razor should only really be applied to theories which recruit the same / evidence / assumptions and generate the same predictions to support quite different conclusions. It should not be applied to compare diverse arguments that recruit vastly different forms of premises and assumptions and generate diverse predictions. Thirdly, the different arguments and theories must be expressed at comparable levels of description, explanation and explicitness. Any ‘theory’ can be made to look simpler if we merely describe it at some meta-level (i.e., a God) relative to an alternative well specified and explicit account (i.e., evolution via a process of mutation and natural selection). These comparisons are not viable forms of argumentation and reasoning and are not appropriate for the application of Occam’s razor. When pseudoscientists attempt to make these types of arguments in an effort to give their views credence, they are being intellectually dishonest.

[Dr B]

some more...........

Occam's razor is at its most useful when it is being used to choose from multiple competing theories – all of which have equal or comparable levels of explanatory power and generate similar predictions. It does not work in situations where the theories being compared are unequal in explanatory power or evidential support, are expressed at completely different levels of explicitness, and make diverse predictions. To put it more succinctly, when there are two (or multiple) competing theories which make exactly the same predictions, the one that recruits only those assumptions which are necessary is the one which is more likely to be correct. It is also more likely that such theories will, as a consequence, be simpler. Note then that the razor, as a principle, can be used to separate two theories that make the same predictions. However, it does not, in any way, rule out the possibility that other theories might make a different though equally evidenced prediction. So, Occam's razor is only concerned with situations where the competing theories are equivalent and where there is no evidence available at this time that could show which one was true. As such it is no more than a reasoning heuristic used to guide thinking in areas where, on other grounds, it may be difficult to distinguish between theoretical accounts.
A further effective use of Occam’s razor is to remove any aspect of a theory that cannot be objectively observed or measured or whose case cannot be argued on logical grounds. Is it really necessary to assume that the mind is separate from the brain in order to explain Near-Death Experiences (NDEs)? Is it really necessary to assume aliens are real based on accounts from alien-abduction experiencers? The answer from science is simple – no! We do not need to assume the mind is separate from the brain to explain NDEs to a reasonably satisfactory level. If we do not need to make this assumption then it follows that it is unnecessary. If it is unnecessary then it can be ‘cut’ from the arguments and theory for NDEs. This will leave you with a more elegant and more parsimonious explanation. Logically speaking, this does not make the ‘mind is separate from the brain’ account false – it merely means that one should not set out assuming something which is unnecessary in the first place. However, as noted earlier there can be controversy over what counts as ‘necessary’ and it is here where the crux of many arguments lie. For the scientist, assuming the mind is separate from the brain is unnecessary as it is not supported by the current evidence. To the Pseudoscientist such dualistic notions are necessary because to them, scientific accounts are insufficient.....snip..........
There is another important issue to keep in mind when trying to apply this principle. A current explanation may recruit only necessary assumptions – but future evidence may extend a theory, thus making it more comprehensive. This process may require the addition of more assumptions which have been shown now to be necessary. As long as an evidenced case for the necessity of reasons and assumptions is made, any theory can be complex as it needs to be. Ultimately any theory needs to be as simple as possible, but as complex as it has to be in order to provide a plausible and comprehensive understanding of the object being studied. This is why a complex theory in and of itself does not violate Occam’s razor at all – as long as all the assumptions are necessary then they must be present in the explanation. Complexity is only a problem if that complexity is unfounded and unnecessary. Therefore, you should only stick to the simplest explanation (only drawing on existing necessary assumptions) until more evidence is provided to the contrary. This can be illustrated nicely with an example. Imagine Theory A makes five assumptions in order to explain an event. In contrast, Theory B makes three necessary assumptions to explain the exact same event (while losing nothing in terms of explanatory power and explicitness). Here, Occam’s razor would state that Theory B is more desirable. It is more desirable as it explains all the data equally well, whilst also making the fewest necessary assumptions.

Finally it is also important to point out that the principle of Occam’s razor, when applied correctly, does not prove a theory is correct relative to another – it merely states that one is less likely to have ones reasoning, argument and theory contaminated by unnecessary assumptions. As a consequence it is more likely to be true (but it is not necessarily proven true).

The principle of parsimony
It is rare to see Occam’s razor referred to by name in scientific papers. However, the principle is very much evident in scientific reasoning and argumentation. Many theorists make arguments for their models based on them being the most parsimonious account available. This is, in essence, an account based on the principle of Occam’s razor. So although students may not see the term ‘Occam’s razor’ being explicitly named in scientific writing – they will encounter regular arguments which recruit the notion of parsimony. A parsimonious account is one that seeks to explain a wealth of complex phenomena by making fewer assumptions. A truly parsimonious account does not sacrifice comprehensiveness at the expense of simplicity – as this would limit the scope of the theory or model. By applying the principle of parsimony we greatly reduce the chance of introducing unfounded and unnecessary assumptions which can have a perverse influence on theorising. This process is, in essence, the application of Occam’s razor.
The reasons for placing the concept of parsimony at the centre of these forms of reasoning heuristics are based primarily on logic and observations from nature. Logically speaking, one is on safer ground with the fewer assumptions one makes as this reduces the potential scope for error....snip...........

the paper continues but that information is not relevant for the present purposes.....

[Mulder]

Are we really to suppose that before Occam, people were constructing scientific theories containing all sorts of redundant and/or unmeasurable elements? And that they had to wait for Occam to put them right?

If the principle is purely one of necessity in constructing theories then I cannot believe it was not already known and used well before Occam.

Quote: "Occam's razor is at its most useful when it is being used to choose from multiple competing theories – all of which have equal or comparable levels of explanatory power and generate similar predictions."

Such a circumstance is so unlikely that I doubt anyone ever feels the need to invoke the principle. Do you have any examples please?

[bobdezon]

Why are you assuming it was unknown before occam? Occam is remembered as postulating this, but that doesnt mean he invented the concept. Your reasoning is flawed.

[Mulder]

My point is that 'don't add in unnecessary bits' to a scientific theory is such an obvious principle that it doesn't need to be specifically postulated by Occam or anyone else.

Here is the Mulder Blunt Instrument, which says: "all things being equal, do not kick yourself while walking". I wonder if it will make me famous?

[Mongrel]

My point is that 'don't add in unnecessary bits' to a scientific theory is such an obvious principle that it doesn't need to be specifically postulated by Occam or anyone else.

Here is the Mulder Blunt Instrument, which says: "all things being equal, do not kick yourself while walking". I wonder if it will make me famous?

If it's that obvious then why do we still see websites about Orbs, homeopathy, magic, zionist NWO conspiracies, phychics......

It's all very well saying "It's obvious!" with the pleasure of hindsight but at the time it must have made enough of an impact to be noticeable or his name wouldn't have been associated with the principle.

[Mulder]

According to Wikipedia: "The origins of what has come to be known as Occam's razor are traceable to the works of earlier philosophers such as John Duns Scotus (http://en.wikipedia.org/wiki/John_Duns_Scotus) (1265–1308), Thomas Aquinas (http://en.wikipedia.org/wiki/Thomas_Aquinas) (c. 1225–1274), Alhacen (http://en.wikipedia.org/wiki/Ibn_al-Haytham) (965-1039), and even Aristotle (http://en.wikipedia.org/wiki/Aristotle) (384–322 BC) (Charlesworth 1956). The term "Ockham's razor" first appeared in 1852 in the works of Sir William Rowan Hamilton (http://en.wikipedia.org/wiki/Sir_William_Rowan_Hamilton) (1805–1865), centuries after Ockham's death. Ockham did not invent this "razor," so its association with him may be due to the frequency and effectiveness with which he used it (Ariew 1976). Though Ockham stated the principle in various ways, the most popular version was written not by himself but by John Ponce of Cork in 1639 (Thorburn 1918)."

He just had good spin doctors!

[bobdezon]

Looks like I was correct then ;)

[Mulder]

I think the term 'Occam's Razor' should be dropped altogether. He didn't invent it, he just used it a lot. And it's bleeding obvious anyway. QED. :smiley:

[bobdezon]

Knock yourself out mate O0

http://petitions.pm.gov.uk/

[Janot]

Ockham did not invent this "razor," so its association with him may be due to the frequency and effectiveness with which he used it (Ariew 1976). Aristotle already had the same idea (Physics, 1.vi) :
The next question is whether the principles are two or three or more in number.... also a finite number is sufficient, and a finite number, such as the principles of Empedocles, is better than an infinite multitude; for Empedocles professes to obtain from his principles all that Anaxagoras obtains from his innumerable principles.

[FarSideOfTheMoon]

I love the principle of parsimony. I'd forgotten that word. You don't see it mentioned much outside academia in my experience.

[Admin]

Dr B's got this one nailed. O0

It's well worth going back and having a close read of his postings there if you wish to get a solid grasp of what this scientific rule of thumb is all about.

[Dr B]

I think the term 'Occam's Razor' should be dropped altogether. He didn't invent it, he just used it a lot. And it's bleeding obvious anyway. QED. :smiley:

If it's so obvious - why don't you understand it? I mean, your first comments on this thread were about simplicity not necessity. So it's not obvious at all to you.

In addition, i think many people throw it around without fully appreciating the context under which it applies. You missed that as well.

Go back and read through the notes carefully - it takes time to fully appreciate the heuristic in it's proper manner. O0

[Dr B]

Mulder

If you go back and actually read what I wrote above you will see the following




Occam's razor (or Ockham's razor as it was originally known) is a reasoning principle attributed to William of Ockham, a 14th century logician and Franciscan monk (ca. 1285-1349). Ockham did not invent the principle – his name became associated to the principle because he used it extensively in his philosophical reasoning.

So your points were addressed before you made them....hhmmmm I must be psychic ;D

[Dr B]

My point is that 'don't add in unnecessary bits' to a scientific theory is such an obvious principle that it doesn't need to be specifically postulated by Occam or anyone else.

The bit that you are not understanding is the bit which states - what counts as necessary? This is where evidence, facts and argument come in. Here we need to make the case for our assumptions and argue why they are necessary. We do this for each assumption.

Remember - it's only a reasoning tool - but a very poweful one for pointing out nonsense arguments - or highlighting which arguments are currently unjustified (i.e., no evidence). This is useful as it helps to focus ones attention on the debate at hand and how to direct your further research. O0

[Mulder]

How on earth can anyone get so much out of "entities should not be multiplied beyond necessity"? If that's really all there is to it then, as I said, it's bleeding obvious and hardly requires pages of interpretation and (dare I say) extrapolation? It's a bit like the way Christians take a couple of phrases out of the Bible and turn it into an entire essay which goes way beyond the original meaning. What is needed is a bit more parsimony. :smiley:

[Mongrel]

How on earth can anyone get so much out of "entities should not be multiplied beyond necessity"?

Because some people study what it means and how it was used rather than arrogantly wave it off with a "Pffft! That's obvious::)"

[Janot]

On a lighter note, does anyone remember the Simpsons episode when the kids in the town go off on a school trip, and the adults all retire to bed for uninterrupted marital stuff? Something happens which results in all the kids returning far earlier than expected, and they all have a different theory as to what has happened to the adults. They insist in constructing a theory which includes all their combined theories, despite Lisa pleading for the application of Occam's razor. Very educational, I thought.

[Mulder]

I've no problem with the contents of DrB's document, as such. I do think it a little wordy and overlong though. I wonder if, given the short attention span and low boredom threshold of today's youth, he might consider a rap version for YouTube?

[Legaleagle]

I've no problem with the contents of DrB's document, as such. I do think it a little wordy and overlong though. I wonder if, given the short attention span and low boredom threshold of today's youth, he might consider a rap version for YouTube?

whatever