mal4mac wrote:So what is the "form".
"Form" (rūpa) is the four great elements, according to the Buddha, but I'm sure that will not help you any further, because you seem to be looking for an explanation you can grasp intellectually. "Form" cannot be understood that way, this is what I'm trying to point out to you. You've come to a point where more words won't bring you clearer understanding, you have to search for the answer what "form" is within your experience. There it is.
mal4mac wrote:Would using Kantian terminology, and transcendental idealism, help at all in understanding this material?
I don't know. Maybe it is useful as a hint.
mal4mac wrote:Is the "form of the tree" the "tree as noumenal object". That is is the "form of the tree" the tree "out there" that we can say nothing about because we haven't, and cannot, experience it?
You approach it from the wrong side. There is no "form of the tree" and there is no tree "out there".
Form does not belong to the tree, but the tree belongs to form. The tree is derived from the experience of form (among other experiences).
I'll try to give you a hint that points to that part in experience where you have to take a closer look at.
The four great elements (mahā bhūta) are earth, water, fire and wind. These elements describe certain experiences. Earth for example is a description for an experience of hardness or resistence one could say. If you experience hardness (earth) as a tactile sensation and examine the whole experience further also taking information of the other senses into account, you may arrive at the conclusion of touching a tree.
BUT it is not a "real tree out there" you are touching, to think that exceeds beyond the sphere of experience, where actually no statement can be made, what you DO know is the experience of form (here earth) and anything derived from form is also nothing but form.
I hope you can follow my poor attempt to give you a hint.
And I hope I don't deviate too far from the topic.
best wishes, acinteyyo