The five skandhas are form, sensation, thought, conformation, and consciousness. Form has a material form; the other skandhas do not. Form is made from the "four" elements; the other skandhas are not ultimately logically able to be characterized. Furthermore,
by the wise the five Skandhas are regarded as thought-constructions, devoid of [dualisties such as] otherness and not-otherness; for they are like varieties of forms and objects in a vision, like images and persons in a dream. As they have no better substance for their support, and as they obstruct the passage of noble wisdom, there is what is known as the Skandha-discrimination.
I'll have two more posts from this chapter; one on sections LIII & LIV and one on LVI.