Errors of perception, like the one you describe, are a common theme in Aristotle. Dysfunctions caused by illness or old age are brought up in De Anima. Imagination is described at DA 428b in distinction to other kinds of false appearances.

Deciding what is a mistake in Kant is more difficult. We don't have the object of representation in hand to compare with another supposed object in the unexperienced bush.

Deciding what is a mistake in Kant is more difficult. We don't have the object of representation in hand to compare with another supposed object in the unexperienced bush. — Paine

That's why I was talking about the possibility of mistake. Instead of insisting that there must be real independent objects, because we perceive objects, as Amadeus seemed to be doing, we ought to accept the possibility of mistake.

But later, he's saying we must pre-suppose them (despite, not being able to know them). — AmadeusD

Kant is right to emphasize that appearances are always appearances of something. But he does not press the consequences of this observation. It sets up a close relationship between appearance and reality and undermines the idea that appearances are entities that exist independently of what they are appearances of. It even suggests to me the somewhat surprising possibility that appearances are, or at least can be, what reveal reality to us, rather than concealing it.

Deciding what is a mistake in Kant is more difficult. We don't have the object of representation in hand to compare with another supposed object in the unexperienced bush. — Paine

"Difficult" is a very mild description for this situation. It suggests that you think that "representation" is not really an inappropriate concept to apply here. But you also (seem to) accept that there is no real evidence for such an object "in the unexperienced bush". So I'm rather puzzled what to make of this.

Instead of insisting that there must be real independent objects, because we perceive objects, as Amadeus seemed to be doing, we ought to accept the possibility of mistake. — Metaphysician Undercover

It's hard to disagree with that. But if we accept that possibility, should we not, by the same token, accept the possibility that there is no mistake. We could then ask which of those possibilities is actually the case. Or even question the framing of the question.

Perhaps I'm not grasping this, but if someone is perceiving "something" then that is "objects" broadly (and in the way i suggest it be used here - I'm not suggesting there are (or that we could know that there are) actual, physical objects beyond the senses). These could simply be that which is required as an assumption for hte perception to obtain. I content roughly that. — AmadeusD

That makes a lot of sense. But you seem to me to be giving with one hand and taking back with the other.
You describe these objects as "actual, physical objects beyond the senses". But since we cannot, apparently, go beyond the senses, these objects turn out to be unavailable to us, which places them beyond our reach. Kant realizes this and so adopts the concept of the object-in-itself or being-in-itself. These concepts are hard to grasp. On the one hand, we know that they exist. On the other hand, we know, and can know, nothing whatever about them. Given that existence is not a predicate, this "knowledge" doesn't seem to amount to very much.
What all this even harder to understand is that physics appears (!) to have provided us with a view of the world that describes objects-beyond-appearances as radically different from what appears to us, on the evidence of what appears to us.
When you say that actual physical objects are an assumption or presupposition, you seem to leave open the possibility that that assumption is wrong - or at least that a different assumption or pre-supposition may also result in a not incoherent alternative conceptual structure. Compare what happens when you abandon the parallel postulate in geometry. We need something a bit stronger than this.

It's hard to disagree with that. But if we accept that possibility, should we not, by the same token, accept the possibility that there is no mistake. We could then ask which of those possibilities is actually the case. Or even question the framing of the question. — Ludwig V

I think the issue is the nature of "representation", and the different types of mistakes which are possible.

Suppose that we consider words as an example of a representation. Mistake could consist of two principal types, mistake in producing (choosing} the representation, and mistake of interpretation. Each assumes a form of consistency whereby inconsistency would constitute mistake.

Mistakes of interpretation are maybe easier to determine, but some, such as those caused by ambiguity, are not so easy because they require an understanding of the intent behind the act of producing or choosing the representation. Other mistakes of inconsistency in interpretation are easier to determine.

Mistakes in producing or choosing the symbol to be used as a representation are more difficult to determine because that requires an analysis of the context, and the intent, to determine whether principles of consistency are being followed.

"Difficult" is a very mild description for this situation. It suggests that you think that "representation" is not really an inappropriate concept to apply here. But you also (seem to) accept that there is no real evidence for such an object "in the unexperienced bush". So I'm rather puzzled what to make of this. — Ludwig V

I figure a representation happens when what is given through sensible intuition becomes an object one can have knowledge about:

The synthetic unity of con-
sciousness is therefore an objective condition of all cognition, not
merely something I myself need in order to cognize an object but
rather something under which every intuition must stand in order to
become an object for me, since in any other way, and without this
synthesis, the manifold would not be united in one consciousness. — CPR, B138

The intuitions are given sensations without which there would be no objects. The things-in-themselves are the result of our activity of thinking about objects. They are not representations of what is beyond experience. They do reflect the given aspect of objects. In that sense, they point to a cause that AmadeusD is calling for. But I cannot refer to the noumena as a cause even if we speculate about it:

The pure concepts of the understanding are free from this limitation
and extend to objects of intuition in general, whether the latter be sim-
ilar to our own or not, as long as it is sensible and not intellectual. But
this further extension of concepts beyond our sensible intuition does
not get us anywhere. For they are then merely empty concepts of ob-
jects, through which we cannot even judge whether the latter are pos-
sible or not - mere forms of thought without objective reality - since
we have available no intuition to which the synthetic unity of apper-
ception, which they alone contain, could be applied, and that could thus
determine an object. Our sensible and empirical intuition alone can
provide them with sense and significance.

Thus if one assumes an object of a non-sensible intuition as given,
one can certainly represent it through all of the predicates that already
lie in the presupposition that nothing belonging to sensible intuition
pertains to it: thus it is not extended, or in space, that its duration is
not a time, that no alteration (sequence of determinations in time) is to
be encountered in it, etc. But it is not yet a genuine cognition if I merely
indicate what the intuition of the object' is not, without being able to
say what is then contained in it; for then I have not represented the pos-
sibility of an object for my pure concept of the understanding at all,
since I cannot give any intuition that would correspond to it, but could
only say that ours is not valid for it. But what is most important here is
that not even a single category could be applied to such a thing, e.g., the
concept of a substance, i.e., that of something that could exist as a sub
ject but never as a mere predicate; for I would not even know whether
there could be anything that corresponded to this determination of
thought if empirical intuition did not give me the case for its applica-
tion. But more of this in the sequel. — ibid. B148

Reading on from here through B159, these limits upon representing things beyond experience are shown to apply to experiences of ourselves:

In the transcendental synthesis of the manifold of representations in
general, on the contrary, hence in the synthetic original unity of apper-
ception, I am conscious of myself not as I appear to myself, nor as I am
in myself, but only that I am. This representation is a thinking, not
an intuiting. Now since for the cognition of ourselves, in addition to
the action of thinking that brings the manifold of every possible intu-
ition to the unity of apperception, a determinate sort of intuition,
through which this manifold is given, is also required, my own existence
is not indeed appearance (let alone mere illusion), but the determina-
tion of my existence* can only occur in correspondence with the form
of inner sense, according to the particular way in which the manifold
that I combine is given in inner intuition, and I therefore have no cog-
nition of myself as I am, but only as I appear to myself. The con-
sciousness of oneself is therefore far from being a cognition of oneself,
regardless of all the categories that constitute the thinking of an object
in general through combination of the manifold in an apperception. — ibid. B159

the different types of mistakes which are possible. — Metaphysician Undercover

That's quite a tall order. But still, if they can all be determined as mistakes, it follows that there must be a truth of the matter, beyond appearances.

Suppose that we consider words as an example of a representation. — Metaphysician Undercover

That tells me a lot about what you mean by "representation". You don't mean that the representation is similar to or resembles or looks like its object. So now I need to know what kind of relationship you think there is between the representation and what it is a representation of.

I figure a representation happens when what is given through sensible intuition becomes an object one can have knowledge about: — Paine

Do you mean what I would call an experience? Something that one might be "directly" aware of? Are you gesturing at a "raw" (uninterpreted) experience? I don't see how anything like that could become a table or a chair. I do think that Kant's point about appearances apply also to experiences - they are always experiences of something; it seems obvious that the object of an experience cannot be the experience, but also experiences cannot also be objects of experience. This is really quite bewilderning.

I'm sorry, but the quotations don't help me.

Kant's terminology is intimidating. I think the way Kant speaks in the Preface to the Second Edition is a good outline to his intentions and what he means by experience, intuition, and cognition:

Hence let us once try whether we do not
get farther with the problems of metaphysics by assuming that the ob-
jects must conform to our cognition, which would agree better with the
requested possibility of an a priori cognition of them, which is to estab
lish something about objects before they are given to us. This would
be just like the first thoughts of Copernicus, who, when he did not
make good progress in the explanation of the celestial motions if he as-
sumed that the entire celestial host revolves around the observer, tried
to see if he might not have greater success if he made the observer re
volve and left the stars at rest. Now in metaphysics we can try in a sim-
ilar way regarding the intuition of objects. If intuition has to conform
to the constitution of the objects, then I do not see how we can know
anything of them a priori; but if the object (as an object of the senses)
conforms to the constitution of our faculty of intuition, then I can very
well represent this possibility to myself. Yet because I cannot stop with
these intuitions, if they are to become cognitions, but must refer them
as representations to something as their object and determine this object
through them, I can assume either that the concepts through which
I bring about this determination also conform to the objects, and then
I am once again in the same difficulty about how I could know anything
about them a priori, or else I assume that the objects, or what is the same
thing, the experience in which alone they can be cognized (as given ob-
jects) conforms to those concepts, in which case I immediately see an
easier way out of the difficulty, since experience itself is a kind of cog-
nition requiring the understanding, whose rule I have to presuppose in
myself before any object is given to me, hence a priori, which rule is ex-
pressed in concepts a priori, to which all objects of experience must
therefore necessarily conform, and with which they must agree. As for
objects insofar as they are thought merely through reason, and neces-
sarily at that, but that (at least as reason thinks them) cannot be given
in experience at all - the attempt to think them (for they must be capa-
ble of being thought) will provide a splendid touchstone of what we as-
sume as the altered method of our way of thinking, namely that we can
cognize of things a priori only what we ourselves have put into them.* — CPR, Bxvi

The text is linked through the citation. The footnote to this passage speaks of being "imitated from the method of those who study nature." Observe how most of the other footnotes in the Preface make similar parallels.

That's quite a tall order. But still, if they can all be determined as mistakes, it follows that there must be a truth of the matter, beyond appearances. — Ludwig V

I don't think so. First, i didn't say anything about how mistake would be determined, only that we ought to believe it is possible. Then, when we look at the primary feature of determining mistakes, mistake is commonly a matter of not producing the desired result. This doesn't imply truth or lack of truth.

So now I need to know what kind of relationship you think there is between the representation and what it is a representation of. — Ludwig V

I think there is a relationship of mastery, like a tool masters the circumstances it is applied to, to produce the desired end. The representation (symbol) is a tool, the living being uses it, and this tool assists the being in survival, as well as making use of its environment toward its ends, and perhaps some other things, dependent on intention.

I don't think so. First, i didn't say anything about how mistake would be determined, only that we ought to believe it is possible. Then, when we look at the primary feature of determining mistakes, mistake is commonly a matter of not producing the desired result. This doesn't imply truth or lack of truth. — Metaphysician Undercover

In general, that's right. It depends on the project. But sometimes the aim of the project is truth, so in those cases mistake does imply the (possibility of) truth.

I think there is a relationship of mastery, like a tool masters the circumstances it is applied to, to produce the desired end. The representation (symbol) is a tool, the living being uses it, and this tool assists the being in survival, as well as making use of its environment toward its ends, and perhaps some other things, dependent on intention. — Metaphysician Undercover

H'm. But it is odd to say that the tool masters the circumstances. I always thought it was the user who mastered the circumstances by using the tool. But isn't there a case for describing the tool as adjusted to or fitting in with the relevant circumstances. A carpenter's saw is good for cutting wood. For metal, you need a hacksaw. Hammers for nails (appropriate in some circumstances). Screwdrivers or spanners in others. Certainly, the enterprise is to adjust circumstances in certain ways; but one needs to recognize what can be changed and what can't.

Kant's terminology is intimidating. I think the way Kant speaks in the Preface to the Second Edition is a good outline to his intentions and what he means by experience, intuition, and cognition: — Paine

That is much more helpful. At least, I seem to be able to get my head round the argument. I wasn't much impressed by the analogy with Copernicus, however. Yet it is an ingenious thought. Maybe there is some sort of parallel. On this reading, my doubts focus on his "a priori" and especially the requirement that the a priori tells us something about the objects in the world. However, I'm delighted to learn that there are objects in the world and that we can know something about them. Some wires may have got crossed between here and the belief that we only know phenomena (are phenomena objects in the world, I wonder) and we cannot know anything (much) about objects or being in "themselves" (unless objects (being) in themselves are not objects in the world.

I believe Kant thought he had uncrossed those wires when he refuted both Descartes and Berkeley with a single blow:

The proof that is demanded must therefore establish that we have experience and not merely imagination of outer things, which cannot be accomplished unless one can prove that even our inner experience, undoubted by Descartes, is possible only under the presupposition of outer experience. — CPR, B275

That supports the statement at B159 that we can know things in the world better than we can know ourselves.

The need for the a priori is to explain why we are built that way. The need becomes necessary by the "altered method of our way of thinking." Otherwise:

If intuition has to conform
to the constitution of the objects, then I do not see how we can know anything of them a priori — CPR, Bxvi

The analogy with Copernicus is to demonstrate how mutually exclusive the two standpoints are.

How some of us went from this location to reading "things-in-themselves" as "mind independent" is a long and winding road through perilous terrain. Time for lunch.

I always thought it was the user who mastered the circumstances by using the tool. — Ludwig V

Perhaps, but I think it is the tool, as the means to the end, which actually overcomes the circumstances. It is more proper to say that the means is what brings success rather than the will. If it was just the will, you could will yourself to success. Instead, success is highly dependent on the tool employed.

But isn't there a case for describing the tool as adjusted to or fitting in with the relevant circumstances. A carpenter's saw is good for cutting wood. For metal, you need a hacksaw. Hammers for nails (appropriate in some circumstances). Screwdrivers or spanners in others. Certainly, the enterprise is to adjust circumstances in certain ways; but one needs to recognize what can be changed and what can't. — Ludwig V

Of course. I recognized this type of mistake when I said in the earlier post, "Mistakes in producing or choosing the symbol to be used as a representation". That would be a mistake of trying to use the wrong tool. We were talking about the different types of mistakes which are possible, and whether each type could be recognized.

The need for the a priori is to explain why we are built that way. The need becomes necessary by the "altered method of our way of thinking." Otherwise:

If intuition has to conform
to the constitution of the objects, then I do not see how we can know anything of them a priori
— CPR, Bxvi

The analogy with Copernicus is to demonstrate how mutually exclusive the two standpoints are. — Paine

We don't know anything of objects or phenomena in general a priori—in terms of what commonalities we can know about all objects without actually consulting particular objects in real time, we must reflect on their general characteristics as perceived. That is we must reflect on prior experience of phenomena in order to see what they all have in common.