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Do thoughts exist? (Yes, I know it depends what I mean by 'existence' but I want that to be included in any answer; another way to phrase my question would be, can you define 'existence' with a plausible definition that would clearly include or exclude thoughts)

If not, then do symbols exist (as symbols)?

Assuming that thoughts do exist, what about ideas, which are not related to specific brain-states or physical processes? Does a thought's existence depend on its physical representation in a human brain, or computer chip, or any other piece of physical reality that encodes for this thought? If not, what about a thought or idea that has never been thought by anyone, or has never been represented in any physical manner in the history of the universe?

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Thoughts exist in the brain, very likely as patterns of transient electrochemical activity.

Although one can imagine various isomorphisms between thoughts and other things (electrical impulses in a computer for instance), until we can actually demonstrate an actual isomorphic process I think we have to withhold judgment as to whether those are thoughts. Details may matter. There certainly isn't anything adequately isomorophic now.

If an idea is an abstraction of a type of thought, then it exists in the sense that a chair exists: particular chairs exist, and one can identify a regularity shared by chairs. But that regularity itself isn't extant; it just tells you how to identify things that are extant. (Thoughts about such a regularity may be extant, just like thoughts about "two" are extant despite there not being a "Two" that exists in the same sense that an apple exists.) One may also wish to identify stored capability to rapidly recall thoughts as "ideas". That seems reasonable, in which case those sorts of ideas act the same way as thoughts: if you have them you have them, and if not you don't.

A potential thought does not exist, just like a potential walk in the park does not. You don't ask "is someone/something in the park because I can imagine walking in the park"? At least, I hope you don't. If you do, pretty soon you're imagining imagining everything and postulating a countable infinity of utterly useless imaginary entities that you wish to say exist. Personally I find this a really poor way to define the concept "exist".

Only when you actually have a thought does it exist. Also, only when you walk in the park are you actually walking in the park.

  • Just to clarify then, the existence of a thought depends on its physical representation? – This lad Jul 4 '14 at 4:51
  • @Matt - As far as anyone can tell, you having a thought is (that part of) the physical process in your brain. There's no other way to get a thought or even something thought-like. – Rex Kerr Jul 4 '14 at 5:02
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    Right, but there's still the possibility (though you disagree, and I upvoted your answer) that an idea exists independent of the physical thought – This lad Jul 4 '14 at 5:04
  • @Matt this relates to my clarifying question that you didn't answer. A thought is by definition a thought of a thinker. If you're defining idea in the same way, then it too by definition is how Rex answers. If you mean something else by the word, explain. – virmaior Jul 4 '14 at 5:18
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There are generally 2 points of views to consider with this question, materialism which rex kerr has elaborated on and idealism which has its origins in Platos theory of forms, which is the basis for modern philosophy of mathematics. He basicly says that reality has 3 structures., the abstract, concrete and the unchanging forms. He says the forms are the true structure of reality, akin to the rigorous proofs that mathematics produces. Furthermore that the concrete reality is an illusion of how this information of the forms appears to sense perception and that the abstract is limited human attempts at true perception of these forms. In this view the only things which truly exist is unpercieved ideas in the form of laws which generate reality. Max tegmark recently wrote a book which he advocates as a theory of everything called 'our mathematical universe' which is categorised as extreme platonism.

  • Hm. I didn't think anyone actually believed in that anymore. I guess I'll have to read Tegmark's work, but Plato's idea of forms strikes me as wildly unnecessary where materialism is adequate and ontologically simpler – This lad Jul 4 '14 at 18:09
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    @Matt - It is wildly unnecessary, but it has a kind of elegance to it that is appealing. Some theoretical physicists are attracted to mathematical beauty above empirical accuracy, but it's certainly not the dominant point of view. – Rex Kerr Jul 4 '14 at 18:37
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If you consider thoughts to be propositional attitudes, i.e. beliefs or desires that are about something (either something real like Paris or something imagined like a unicorn), then there are at least one important materialist alternative to Rex's response.

Common sense tells us that our brains must store thoughts about stuff in a manner that is similar to natural language (called the "language of thought" hypothesis. It is this "language of thought" hypothesis that is typically considered to be the currency of how our brains reason about things, and the popular functionalist theories of the mind assume this to be true.

Just one problem: neuroscience is struggling to reveal how this is supposed to work in the brain. Take Alex Rosenberg's description from The Atheist's Guide To Reality: Consider thinking about Paris: how does your brain know which neurons encode information about Paris? It must ask some other part of the brain to go find the location of the Paris neurons - let's call this other part the "neural interpreter". But the question then becomes: how does the neural interpreter know which neurons encode information about Paris? It must ask some other ... and we have an infinite regress.

Funtionalists and identity theorists hold out that neuroscience will one day find a solution to this problem, but eliminative materialists like Paul Churchland and Alex Rosenberg claim that this proves that our brains do not and can not encode and act upon information in the form of a "language of thought". It is merely an illusion that you are thinking about Paris (or anything at all), a useful narrative that your mind is generating as part of its evolved mechanism of making sense of the world. EM's consider propositional attitudes to be a radically false theory of mind.

According to EM's, thoughts do not have real existence insofar they are propositions about things.

  • Since when has common sense been a good guide to neuroscence? "It's common sense that we have three photopigments in our eyes even though can see a continuum of colors". "It's common sense that our visual scene is decomposed into a a bunch of edges of different sizes and orientations, with presence encoded as discrete spikes of voltage." etc. etc.. At some level there is a language of thought (we are aware of an internal narrative), but that doesn't mean it must be at every level, just like there are "web browsers" at some levels of description of computers but not others. – Rex Kerr Dec 7 '15 at 22:39
  • Common sense is not a good guide to neuroscience (my point)! The eliminativists hold that "language of thought" is an illusion created by our mind's desire to put a narrative on our inner processes. It has no more real existence than unicorns or santa clause. – firtydank Dec 8 '15 at 10:52
  • It's also as illusory as your perception of a chair. It's all in your head at that point. Otherwise, no, I disagree. There is an internal dialog that can be used to help think about things and this is unlike that there is not an external unicorn that can help save a princess. That it is not irreducible is a different statement than that it is an illusion! – Rex Kerr Dec 8 '15 at 15:36
  • Rex, I pointed out an alternative view, held by philosophers holding chairs in respected institutions, on the reality of thoughts. I've given a reference to one of their works if you are interested. I'm not going to try to defend it. If you think I misrepresented it, please point it out. If you disagree with them, please take it up with them. – firtydank Dec 9 '15 at 7:26
  • I'm not disagreeing with them but with your characterization of them. (Well, Paul Churchland, anyway. I'm not that familiar with Alex Rosenberg.) In particular, the notion of "illusion" is too strong as you appeared to use it (i.e. no substantive difference between a language of thought and a thought of a unicorn). – Rex Kerr Dec 12 '15 at 1:17
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I think it depends on how you define 'exist'. If you consider the Universe to be only material in structure, then thoughts cannot exist, because they are 'abstract' objects. But if you think of the Universe as having both material and abstract components (dualism), then you could say that thoughts exist within its abstract realm - and you might go as far as saying that thoughts can be considered objects with form, that maintain unique positions within this abstract realm, and interact with nearby thoughts. You might also go as far as theorizing that thoughts are objects that are subjected to a form of 'abstract' gravity.

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In Physics VII.3 (247b20):

The same goes for mental states as well. They too exist because they are in some way or another relative to something...

Which exists, presumably; the man or person; this 'relative' is, I think, somewhat like supervenes - but I'm on relatively unknown ground here.

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Whatever else a thought be, whether it be a neuron firing in the brain as Rex suggests (which is itself a rather controversial claim) or some immaterial activity, it seems that it is entirely self-contradictory to deny the existence of thought of some kind, so long as we believe thought to be that which we are doing when we ponder concepts or the like. Thought should not be confused with the object that is thought about; thought can be about anything, because thought is not necessarily an object in itself, but rather an activity or power (and thus Rex's nonchalant categorization of thought as some physical object seems to me to be rather unjustified). But this power and activity needn't rely on the reality of its objects to be considered to be real; the thought of a phoenix is just as real as the thought of turtles. This is because the existence of thoughts must be assumed, since there is quite simply no way in which we can possibly deny their existence so long as we think anything at all.

What you call 'idea' I would call 'concept'. A concept is a specific object of thought. Concepts exist independent of any one person thinking of them, and even the entirety of people thinking of them. This applies even to nonexistent concepts, such as the phoenix. The phoenix can be rethought of by any number of people, and even if the entire human race were to go out of existence tomorrow, we could come back into existence and think again of a phoenix. This illustrates that the concept of phoenix is firstly not dependent on any specific mind to think it up, nor can thoughts as such be said to be necessarily conjoined to concepts. The existence of concepts themselves seem to be as self-evidently existent as thought (and indeed I would argue that one cannot be said to loosely exist without the other). But the existence of concepts in terms of the instantiation of their supposed properties rather than merely the instantiation of their propositions is another matter entirely (one that is surely a specific endeavor rather than general). As to symbols, it is coming to be realized in more up to date philosophical circles that the reduction of thought to talk of symbols or computer programs fails in all kinds of ways.

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