As I discuss in this question, by far the most popular school of Hindu philosophy is the Vedanta school, which bases its tenets on the doctrines laid out in the Brahma Sutras, a work by the sage Vyasa that summarizes and systematizes the philosophical teachings of the Upanishads. But before the time of Adi Shankaracharya the dominant school of Hindu philosophy was the Purva Mimamsa school, which I discuss here. In contrast to the Vedanta school which is devoted to analyzing the Jnana Kanda of the Vedas, i.e. the Upanishads, Purva Mimamsa focuses on analyzing the Karma Kanda of the Vedas, i.e. the Samhitas and Brahmanas.
Now almost all members of the Vedanta school other than Advaitins believe that the Jivatma or individual soul is atomic in size, in contrast to Brahman who is omnipresent. And the only reason Advaitins differ is they see the Jivatma and Brahman as the same, and Brahman is omnipresent. Still, all members of the Vedanta school can at least agree that there's only one Atma which is omnipresent. But the Purva Mimamsa school had a very different view. Let me explain.
Shabaraswami's Bhashya is the canonical commentary on Jaimini's Purva Mimamsa Sutras, the defining text of the Purva Mimamsa schools. In this excerpt from his Bhashya, Shabaraswami argues that since actions no longer exist when they're finished, it follows that actions create an Apurva or unseen entity which later brings about a positive or negative result. But then an objection is raised, what if actions continue to exist in the souls of the people who did them? Shabaka responds that this is impossible, because actions require motion and souls cannot move because they are omnipresent:
If it be argued that "on the strength of the declaration of a certain result following from a certain sacrificer, it may be presumed that the act of sacrifice itself does not perish (but continues to exist till the appearance of the result)", - the answer is that such a presumption cannot be right; because of the Act itself we do not perceive any other form; as a matter of fact, that alone is called an "act" which transposes its substratum from one place to another; and no such transposition is possible for the Soul, - because the Soul is omnipresent; that the Soul is present in all places is indicated by the fact that its functioning is found everywhere (in the shape of experiencing pleasure, pain, etc.)
So Shabaraswami, and the Purva Mimamsa philosophers who came after him, believed in a theory of multiple omnipresent souls. For more elaboration on this theory along with logical arguments for it, see this excerpt from Kumarila Bhatta's Tantra Vartika. In future I may post a question examining these arguments, but for now I'd like to ask something a bit more concrete. My question is did Shabaraswami invent this theory of multiple omnipresent soul? Did any philosophers before Shabaraswami, inside or outside of the Purva Mimamsa school, mention or support this theory?
If it helps, this book says that Shabaraswami lived somewhere between the 1st century BC and the 6th century AD. But the traditional Hindu dating may differ from this Western dating.