I meant to say that taking intuition of space and time as a process of my perception raises the question of how "objective" it is. That ties into Kant's beef with Berkeley who treats space as an experienced phenomenon. Kant argues that it is, rather, an a priori condition for sensibility: — Paine

Space and time are big issues in philosophy, and I'm not an expert. But I do agree that we do not experience space as a phenomenon. I wouldn't say that it is a condition for sensibility, but rather a principle of interpretation of the phenomena.
I'm afraid, though, that I simply have no grasp of what he means by saying that it is an intuition. Is it something like a brute fact?
My other problem is how we can conceive of space without objects in it, when we cannot conceive of what I call objects without their spatial dimensions and position in relation to each other. The mathematical representation of space - as a graph with three axes and an origin seems to separate space from what it contains, but I think that is an illusion. The graph has no meaning except as a way of locating objects.
I realize that a priori means before experience, but what does the metaphor mean here? (I realize that it is a deeply embedded metaphor that has become a regular way of speaking. But I detect an ambiguity here, whether before means a stage in a process or a position in a structure, supporting or enabling experience. My metaphor for understanding the a priori is framework vs content, setting up the rules of a game vs playing the game. I think that that Kant thinks that the a priori tells us something about how the world is - about possible worlds.

The principle that throughout dominates and determines my Idealism, is on the contrary: "All cognition of things merely from pure understanding or pure reason is nothing but sheer illusion, and only in experience is there truth." — Prolegomena to Any Future Metaphysics, page 374, or page 69 in the linked document

My word. That is a surprise. He sounds like a radical 20th century analytic philosopher.

Space and time, together with all that they contain, are not things nor qualities in themselves, but belong merely to the appearances of the latter: up to this point I am one in confession with the above idealists. But these, and amongst them more particularly Berkeley, regarded space as a mere empirical presentation that, like the phenomenon it contains, is only known to us by means of experience or perception, together with its determinations. I, on the contrary, prove in the first place, that space (and also time, which Berkeley did not consider) and all its determinations a priori, can be known by us, because, no less than time, it inheres in our sensibility as a pure form before all perception or experience and makes all intuition of the same, and therefore all its phenomena, possible. It follows from this, that as truth rests on universal and necessary laws as its criteria, experience, according to Berkeley, can have no criteria of truth, because its phenomena (according to him) have nothing a priori at their foundation; whence it follows, that they are nothing but sheer illusion; whereas with us, space and time (in conjunction with the pure conceptions of the understanding) prescribe their law to all possible experience a priori, and at the same time afford the certain criterion for distinguishing truth from illusion therein. — Prolegomena to Any Future Metaphysics, page 374, or page 69 in the linked document

This just defeats me. Perhaps you can paraphrase it for me?
".... space ..... can be known by us, because .... ... and makes all intuition of the same (i.e. all perception and experience) ....possible."
Well, yes, with reservations.
Does "space .... and all its determinations a priori," mean Geometry?
What does "(sc. space)inheres in our sensibility as a pure form before all perception" mean?
"... experience, according to Berkeley, can have no criteria of truth, because its phenomena (according to him) have nothing a priori at their foundation"
"...space and time .... prescribe their law to all possible experience a priori, and at the same time afford the certain criterion for distinguishing truth from illusion therein."
That's roughly the definition of the a priori, using a metaphor, which I think clouds his meaning. The kind of law that is a prescription defines the possibility of breaking it. But if the a priori defines possibility, there is no possibility of breaking it.
I would need some argument to accept that space and time are the criterion for distinguishing truth and illusion. I would have thought that non-contradiction and identity would be essential - or is that what he means by the "pure conceptions of the understanding."?

I, too, am learning from this discussion. — Paine

That's all right, then.

I will try to respond to some other of your comments but need to get back to painting a specific appearance. — Paine

I see from later comments that you are painting a door. That's a hard task, because a vertical surface promotes drips. I was, however, rather surprised. I always thought that the only way you could paint an appearance was by painting a picture.

It's true that by existing, we effect things, and perception influences our surroundings. The observer effects what it observes.

Quite right about the 'a' being a footnote and not an indefinite pronoun. One of the hazards of copying and pasting text here. I try to clean those up as a rule. With Kant, it is like herding cats.

Your points about how the use of appearance became more strictly expressed through later works is well taken. Thank you for connecting the A379 language to that of B157. The corresponding pages of the Editors Notes are 739 and 727. For others following the linked edition. It is from those notes that I remembered the passage from Prolegomena above.

I have been reading what is said in A379 through the lens of the Refutation of Idealism given in the B edition. I was thinking that the specificity is still focused upon the difference between what is given through inner and outer intuitions when the Theorem states:

The mere, but empirically determined, consciousness of my own existence proves the existence of objects in space outside me — B275

That also, as you said:

tacitly supports Descartes’ sum while not being quite so supportive of the “problematic” idealism explicit in the cogito ergo… part — Mww

I will have to mull over whether the Theorem is "not so supportive" or a thumb in the eye to the other part. I have been leaning toward the latter.

One element in both the A and B editions that is fairly consistent is the term 'transcendental object.' It is used 28 times in the text (according to my find-in- page function). The meaning as the "unknown ground" for both the inner and outer seems to be preserved at each passage.

I will continue to think about the role of the "I am" that you illuminate.

Space and time are big issues in philosophy, and I'm not an expert. But I do agree that we do not experience space as a phenomenon. I wouldn't say that it is a condition for sensibility, but rather a principle of interpretation of the phenomena.
I'm afraid, though, that I simply have no grasp of what he means by saying that it is an intuition. Is it something like a brute fact? — Ludwig V

Before trying to respond to that, it would help to know which thinkers you are well versed in. Kant was using the language of his contemporaries. I know some things about them and their differences but studied Ancient Greek philosophy before and more rigorously than turning to Kant's time. I am still a stranger in a strange land.

All the thinkers Kant responded to had different ways of framing what is intuition, phenomena, ideas, logic, and categories. They were arguing within a set of parameters. The problems we have looking in from outside is that we cannot share that set without problems of translation.

With that said, where are you coming from?

I'm fairly typical of people educated in the 20th century English-speaking philosophical tradition. But with an emphasis on ordinary language philosophy and Wittgenstein (especially the later Wittgenstein) and Locke, Berkeley and Hume, so very sceptical of analytic philosophy. Some Ancient Greek Philosophy, but mostly early to middle period Plato and Aristotle's ethics. Some continental philosophy, especially existentialism. I was not active philosophically from 2000 to 2020 so considerably out of date.

All the thinkers Kant responded to had different ways of framing what is intuition, phenomena, ideas, logic, and categories. They were arguing within a set of parameters. The problems we have looking in from outside is that we cannot share that set without problems of translation. — Paine

I'm not surprised. There's always a delicate balance to be struck there.

Thank you for the report. I will work on painting a picture.

Here's a question I would like to put to you.

I found the following in SEP - Kant

The two-aspects reading attempts to interpret Kant’s transcendental idealism in a way that enables it to be defended against at least some of these objections. On this view, transcendental idealism does not distinguish between two classes of objects but rather between two different aspects of one and the same class of objects. For this reason it is also called the one-world interpretation, since it holds that there is only one world in Kant’s ontology, and that at least some objects in that world have two different aspects: one aspect that appears to us, and another aspect that does not appear to us. That is, appearances are aspects of the same objects that also exist in themselves. So, on this reading, appearances are not mental representations, and transcendental idealism is not a form of phenomenalism.

That makes a lot of sense to me, and would resolve many of the objections that I've been raising. What, if anything, do you think of it?

The writer of the article is assuming that things-in-themselves are present whether we experience them or not. That is not what Kant says in the quote given in the preceding section:

What may be the case with objects in themselves and abstracted from all this receptivity of our sensibility remains entirely unknown to us. — A42/B59–60

When the writer says in section 3,

In some sense, human beings experience only appearances, not things in themselves. — ibid

experience is taken to be a matter of contact with either one or the other kind of object. The narrowness of that reading is what I argued against in my comment to you here. There is a ground where the inner and outer are thought to be in one world, but it is not presented as only things outside of us. The writer is unknowingly presenting a two-object interpretation: Objects in the world and our representations of them.

The writer continues the misunderstanding in 3.1. What is being called a "two object interpretation" by the "so-called Göttingen review by Christian Garve" is what Kant vehemently denounced in the Prolegomena passage I quoted previously