Valdas: “When you try to describe something-in-itself then what you are doing is putting into thought the reality you perceive of the object.”
Faust “the characteristics that we can perceive are the ones we know…”
These sound the most like what I understand of Kant’s position.
For Kant, all we can know is appearances (ie, phenomena) and possible experience of them. But the concepts that we use to understand and know the objects of phenomena can be used to speculate about objects in themselves (‘behind’ phenomena and possible experience). These might be quite precisely like that suggested by appearances; or they might be radically different (specifically, without space, time, substance, or causality). But we can’t ever experience it, or understand it with any certainty (ie, know it).
Chimney Sweep: “I believe that “mapping” from the phenomenal world to the “noumenal world” constitutes the prime challenge of all philosophy”.
In Kant’s sense of ‘the thing in itself’ this wouldn’t be possible; we can, however, coherently map a course from actually known phenomena to further potentially knowable phenomena (ie, possible experience).
I’m think things in themselves and the noumenal exactly correlate though - noumenal means something like ‘mental’. Hence why mental speculation about things in themselves is possible, highly tempting - but irresolvable.
Impenitent: “I have lots of opinions, but they are things in themselves and you can’t have access to them…”
Wittgenstein (who was influenced heavily by Schopenhauer) turned the notion of the thing in itself into what was beyond the limits of language. (So obviously, he kept his trap shut about it, usually). Anway, for him opinions which you cannot express would be truly private experiences (as opposed to public language and communicable experience) - so maybe things in themselves in the classic sense.