The anology with chemistry (Elements and compounds) can also help understand the discussion in the Mahabhashya regarding whether a word is substance (द्रव्य) or form (आक्रुती) because the ideation of the Maheshwar Sutras as well as the Ashtadhyayi by Panini as well as Patanjali are substantative.
The question of the parallels of the analogy hover around the following points.
1) Whether a letter, word or sentence is only a substance.
2) Whether a letter, word or sentence is only a form.
3) Whether a letter, word or sentence is both substance and form.
4) Whether a letter, word or sentence is neither of the three above and is only sound.
5) Whether a letter, word or sentence is 'Daivi' and the above four aspects are non consequential?
The answers to the above question will determine how we see the Maheshwar Sutras and the Ashtadhyayi.
My study of the Maheshwar Sutras tells me that a letter, word or sentence has both substance and form.
Why? Because of the difference between a Sutra and an alphabet. The Maheshwar Sutras as the name suggests are Sutras whereas अ, आ ,इ, ई ...... क, ख,.ग, घ is the alphabet.
What is the difference?
A Sutra tells both the lakshya and the lakshana in one stroke. On the other hand an alphabet restricts itself to describe a sound in arthographic form.
Patanjali has discussed the above aspects in his own way. Panini for one has put the subject in sutra form. Our job is to understand what they wanted to convey and experience it.
Thoughts on the subject are welcome.
With regards,
Achyut Karve.