If ontological idealism is correct, a brain is an idea among the others. Then why if we modify (the idea of) a brain, the whole mental world changes accordingly? Why is there a mental representation (the brain) that, if modified or eliminated, brings with it all the others? How can an idealist explain this asymmetry?

  • Good question, you're on the right track when you question the brain as anything other than a body maintaining and data storage device! CS
    – user37981
    Commented Mar 28, 2019 at 14:10
  • Under ontological idealism ideals and mental representations are different things. The claim of idealism is merely that what the world is made of is more like mind than matter, there is nothing wrong with some of that stuff supporting mental representations, just as the matter does for materialists.
    – Conifold
    Commented Mar 28, 2019 at 20:04
  • @Conifold I can’t grasp the difference between ideals and mental representations Commented Mar 28, 2019 at 21:07
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    "Ideals" should be "ideas", sorry for the typo. Just as not all matter is brain matter, not all ideas are mental representations, or mental at all, at least not to idealists. Plato certainly did not think that his Highest Good or Justice are the result of re-presenting something else to a lowly someone like us, let alone mentally. They are self-standing forms of immaterial sort. Of course, we typically think of ideas as ideas in a mind, but you should not take the word "idealism" too literally.
    – Conifold
    Commented Mar 28, 2019 at 22:31
  • Why should it not?
    – Cort Ammon
    Commented Mar 29, 2019 at 5:36

1 Answer 1


"The physical is simply the verifiable contents of perception, a particular category of experience. As such, what we call ‘physical interference with the brain’ is simply the extrinsic appearance of experiential activity external to an alter that, in turn, disrupts the inner experiences of the alter from across its dissociative boundary." Bernardo Kastrup, The Idea of the World (pp. 85-86).

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