The Tattvārthasūtra does not define the substances by what they are made of. It defines them by what they do for the rest: motion, rest, room, the body and its breath, the help souls give one another, and change itself.
Sūtra 5.17: the help of dharma and adharma is motion and rest. 5.18: the help of space is room. 5.19: the help of matter is body, speech, mind and breath. 5.20: and pleasure, pain, life and death. 5.21: the help of souls is to one another. 5.22: the help of time is becoming, change, activity, before and after. The word each time is upakāra or upagraha - a help given, not a cause that compels: the water does not move the fish, the shade does not stop the traveller.
The view sets the six as columns with the sūtra's attributes down the side - how many, how many space-points, with form or not, with extension or not, active or still, where - and the function and the bhāṣya's likeness at the foot of each. Read across and the pattern is plain: three of the six are one substance apiece and do nothing but make the other three possible.
The six, compared as the sūtra compares them - What each does highlighted
Measurements and counts
jīva
souls help one another - 5.21
pudgala
body, speech, mind, breath; pleasure, pain, life, death - 5.19–20