On our now not so recent episode about Berkeley, with David Hilbert,  I said in passing that idealism, in some form or other,  is permanently tempting.   Don't get me wrong,  I don't believe in idealism.  I consider myself a realist and a physicalist.  Not only do I think that the world is (largely) independent of mind.  I also think that the mind is ultimately just a part of that mind-independent world.   That is,  the mind is ultimately built out of and reducible to stuff that is not yet mind.   Or so I would argue.   So I don't come here to defend idealism.   Neither do I come to refute it -- not  exactly anyway.  Lots of philosophers  have claimed to have decisively refuted one form of  idealism or another, but   I suspect that such decisive refutation is probably not to be had.    Although I don't for a second endorse idealism,  I think it is worth ruminating on its (dark)  allure  just for a bit.

Idealism is a mansion containing many different rooms, some more elegantly furnished than others.  Berkeleyan idealism, the ur-form of idealism, is a pretty spare  thing compared to   Kant's  "Transcendental Idealism"  which we will no doubt explore a bit to day on the show.    Though the latter has sometimes been said to be just a  fancied up form of  Berkeleyan idealism, that construal does inadequate justice to the richness and complexities of Kant's philosophy.  Kant's  understanding of the constructive and combinatorial powers of the human mind vastly exceeds anything on offer in Berkeley's philosophy.   Indeed,  despite the fact that I reject his transcendental idealism,  I tend to think of Kant as an early and great cognitive scientist.  He was really an amazing student of the human mind, much more astute than John's favorite philosopher David Hume  -- though Hume, too, had many deep and lasting insights into the mind.

After Kant, Idealism, especially in Germany,  takes on many and variegated forms.  Though our show on Shchopenhauer touches on one form of post-Kantian idealism,    I can claim no expertise in this rich period in the history of philosophy.     I do currently chair a department that has perhaps the single best collection of scholars of German Idealism in the English speaking world.  Whether that's blessing or a curse,  I'll leave to others to judge.   This preface is just a way of warning you that I myself am content to  paint with a very broad brush here.   If you really want to know about the many rooms in that  philosophical mansion called Idealism,  I'm not really  the right  philosopher to serve as your guide.

Idealists of all varieties  seem to share  a certain deep puzzlement over how "transcendental realism" could even possibly be true.   By transcendental realism I mean, roughly, the view that our "ideas" somehow represent,  give us cognitive and perceptual access to, and thereby enable us to think about and perceive  a world not of the mind's own constituting and not in any sense contained within the mind.

Why should anybody find the idea that we perceive and think about a world not contained within mind and not entirely of the mind's own constituting  at all puzzling?    Isn't it the most natural thing to believe that there is something "out there" to which our thoughts and perceptions somehow manage to give us access?

Apparently not.  Historically, perhaps the  puzzlement starts with the "idea" idea.   The idea idea has a couple of different components that make idealism a tempting option.  First, there's the thought that ideas are some sort of inner mental occurrence.   Next there is the thought that ideas represent what they represent by "resemblance."   One then rather quickly notices that  an idea is bound to resemble some other idea more than it resembles any non-idea.   It's a pretty short step from there to concluding that our ideas never "resemble" any mind-external reality and so can never represent any mind-independent reality.

This admittedly  quick little  argument  doesn't begin to do justice to the subtlety of various actual arguments for idealism.   But since not  much of  the  remaining allure of idealism in the 21st century is depends on arguments directly tied to the idea-idea,  I won't  try to do better justice to the detailed arguments for idealism that start from the idea-idea.   The idea-idea, especially, its resemblance theory of representation,  fell out of repute long ago.  Kant, for example, had already rejected it and replaced talk of ideas with talk of "concepts."   Thoroughly modern representationalists have many views about how representations connect up to reality,  but mostly they don't go in for simple resemblance theories thereof.   Some  take linguistic representations to be the paradigm of a representation, for example.  The word  'snow'  doesn't  resemble snow in any interesting ways that I can think of but it "stands for" snow nonetheless.

So what  could tempt one to idealism if one rejects the idea-idea and its resemblance theory of representation-represented relation?    One possible answer is connected to belief in what I call the priority of the representation over the represented.   If you think, as many philosophers do, that all of our episodes of thought or perception involve deployment of inner representations of some sort,  you might think that it's impossible to "step outside" the representations.   We have always to do with our own representations and never with a bare object.  If objects are ever present to us in either thought or perception, they are present only through our representations themselves. (Something like this insight is at the core of Kant's own transcendental idealism, by the way.) 

This way of thinking doesn't yet give rise to any particular form of  idealism, to be sure.  Many representationalists are also realists.  But if we ask  just what an object is,  a certain way of looking at objecthood leads pretty naturally to some form or other of idealism.  You could think -- though I don't think you should -- that an object is just whatever is "represented"  by certain sorts of representations, representations that play a certain role in an overall system of representations.    Never mind exactly for now just which sorts of representations and which roles.    But if you think the role playing representations somehow precede and determine the objects, rather than following and being determined by them,  you've taken a first step toward idealism.   

Idealists tend to think that   the very concept of an object is nothing but the concept of a something that is tied to our representations in a certain way.  And they tend to think that this is some sort of  a priori truth about our representations.   If you start thinking this way, you could quickly get yourself into believing that "objects" are just a sort  projection from or construction out of our representations and relations among them.   

Why should anyone believe in the priority of the representation over the object?  Idealism starts with a kind of "how else could it be" impulse.  Think about it this way.   We realists tend to think that our representations  sometimes manage to "match" a world that is entirely independent of us.  But this "external" world  is supposed to make itself manisfest to our minds, realists admit,  only through its relentless rush upon  the portals of sensation.   But this inward rush, the realist will also have to admit,   is really just bare energy that does nothing but energize our nerve endings.   It's not as though through the inward rush upon sensation the external world somehow directly "imposes" truth tracking representations upon us.    As Berkeley puts it somewhere the "external" world does nothing to the eye except to shake the optic nerves.  Yet, somehow the energized shaking of our nerve endings gives rise to a vast and varied plethora of representations -- representations of time, space, cause, effect, persistence, change, and on and on.    How does the mere energized shaking of our nerve endings manage that?   

One only need read, say, Hume, to convince oneself that these representations can't quite be "derived"  or "deduced"  or even "induced"  from the bare inward rush of energy upon the portals of sensation.   They go beyond -- way beyond --  anything merely "given" in sensation.   If you accept that Humean conclusion you might be tempted to conclude that a our representations as of  an "external world" of objects  arrayed in space, rushing in upon the portals of sensation,  is some sort of illusion and that many of our  representations are  groundless and deserve to be abandoned.  In some  moods, Hume seems to flirt with such the view that many of our representations as of an external reality  are groundless.  But his finals views are actually quite subtle.

An alternative path from Hume's insights -- which are genuine insights -- is represented by Kant.  (Kant claims, by the way, that reading Hume awoke him from his "dogmatic slumber.")  Hume is right, according to Kant.   We don't derive our representations of cause, effect, persistence, change, space or time from the inward rush of sensation.  Rather, we impose them upon the inward rush and thereby "constitute" or "create" the world -- at least the world that we experience -- which is the only world that we can know.       The representations of space, time, cause, effect, persistence are already resident in the mind,  prior to the inward rush.  They are deployed by the mind to "organize" the inward rush.   In organizing the inward rush via these pre-given representations,  we structure and order the world.  The structure and order that we impose on the inward rush is not there before we do our thing.  It's not something we find in the inward rush.

Why is this a tempting idea?   In large measure its allure results from the its promise to explain, in a way that few competing theories do,  just how we mamage to cognize a highly complex, structured and ordered world,  on the basis of the meager deliverances of "brute" sensation. 

It comes with a cost, though.  If the order and structure we cognize in the world is merely the mind's own imposition,  that means we can't really know anything about the world "in itself."   Indeed,  it's fair to wonder how an idealist, even a Kantian transcendental idealist,  can believe in the existence of a mind-independent world at all.   

Personally,  I find that an inordinate cost.  But this is not the place to talk about how we can avoid paying that cost.