We can read for the definition of idea, in the Cambridge dictionary:

a suggestion or plan for doing something:

I've had an idea - why don't we go to the coast?
"Let's go swimming." "That's a good idea!"
If you have any ideas for what I could buy Jack, let me know.
That's when I first had the idea of starting (= planned to start) my own business.
I like the idea of living in the countryside but I'm not sure I'd like the reality.
She's full of bright (= good) ideas.
[ + to infinitive ] It was Kate's idea to hire bikes.
It's not a good idea to drive for hours without a rest.

I think everybody has an idea about what ideas are. Plato's idea is (was?) that they live in some ideal world or space and that they cast shadows in the real material world. We can never have a full picture of these ideas but they can be examined by examining the shadows they cast. We can examine the idea of a circle but we are never able to construct an actual one.

According to Plato mathematics comes close to knowing the ideal ideas ideally. The idea of one of the Platonic geometrical objects (the cube, the tetraheder, etc.) is exactly what they are. A constructed cube is always stained, dusty, or badly formed and is a step from reality. In this respect,

Aristotle thought exactly the opposite. He thought that the idea was a step away from reality, which shows things as they are: muddy, dusty, stained, or stoned. You can try to remove all this from the object at hand and like this an idealized version will appear though this is still an object. It is not something corresponding to an idea in the ideal world.

How is an idea to be viewed? Is it something that really exists, like brain processes? Is it an object that forms the ideal object of another object? Or is it something that exists in a world of ideas only? Are there views different from these of Aristotle or Plato?

  • 2
    Since the middle ages ideas became "universals" and now "abstract objects" are more commonly used. The debate over the nature of universals is perennial, and there is no point to replaying it here. If you want a general overview see the linked articles, questions for this site need to be more focused and definitive.
    – Conifold
    Commented Jul 9, 2021 at 18:54
  • @Conifold I think ideas are processes going on in the brain. Corresponding to processes in the physical world. They are both physical processes. Both processes may refer to an ideal world, like Plato thinks, in opposition to Aristotle, who views ideas as brain processes (though he didnt knew about these yet). These ideas may shape the real physical world and really adapted stuff is the ideal stuff. Commented Jul 9, 2021 at 19:12
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    This is not a site for discussions of what users think or come up with, it is a Q&A site with answers to be based on published literature. What you need is a discussion forum like The Philosophy Forum.
    – Conifold
    Commented Jul 9, 2021 at 19:17
  • @Conifold Thanks for the link! I must take a further look there! In this question though I ask about other ideas than the ones of Aristotle and Plato. Commented Jul 9, 2021 at 19:21
  • consider also philosophy.stackexchange.com/questions/77950/…
    – sand1
    Commented Jul 9, 2021 at 20:44

2 Answers 2


First of all, ideas are entirely dependent on brain processes. You have a pattern of neural activity which can be interpreted as an idea, in the same way that a pattern of water molecules can be interpreted as a crashing wave (if it has the right arrangement).

The mind is not the same as the brain; the mind is an abstract model of a part of what the brain does. It is like the relationship of the physical seven bridges of Königsberg to the abstract graph of the bridges. We can interpret what the brain does as mental activity, in the same way we can interpret what water molecules are doing as wave activity. The water molecules are neither physically separate from the wave, nor are they the same as the wave. The wave is an abstraction over the water molecules.

So, our abstraction of the mind has pieces called "emotions" and "ideas" and "sensory data" and "motivations" and so on. These pieces are all abstractions of actual physical neural activity. The abstractions have a certain causal structure, where emotions and ideas influence other ideas, a structure which is mirrored in and dependent on the causal structure of the brain. An idea is a certain kind of piece of this abstraction of the mind.


Here's my take from Naturalism and physicalism, and minimal or no mind-body dualism

All mental activities, which includes forming ideas, are brain processes. A Platonic ideal like a perfect sphere is first an activity in someone's brain. Someone who knew your brain well enough could in principle observe you thinking about a such a sphere. It is a mental state.

We are born with zero a priori knowledge about the external world. However, we are born with a nervous system, senses, and brain that connect to each other in a set way. It is that internal system of senses and brain interacting which we use consciously and unconsciously to interact with the world to build up all external knowledge. How brains get to thinking and rationalizing and imagining ideas is because we are able to detect (through our senses) real patterns about the world. Our brains, due to the evolutionary benefit of saving energy later, also evolved to extrapolate from observed patterns. We witness object permanence, sums, and addition early on from counting apples, and our brains internalize those rules and try to apply them further.

So an ideal sphere is a brain process where someone is imagining in their brain the perfect version of what they have witnessed only imperfect versions of through their senses. It is no more and no less. This seems closer to Aristotle then Plato.

  • I like the answer but I dont agree with us being born without prior knowledge. Commented Jul 9, 2021 at 19:17
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    @DescheleSchilder Maybe I should have said, we are born with (unconscious) knowledge of how our senses connect to each other and to our brain. It is that "known" system we then use to interact with the outside world, which we have no a priori knowledge of. Added an edit to include this
    – J Kusin
    Commented Jul 9, 2021 at 19:20

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