When it comes to determining what Patañjali did, the uncertainties continue. A first achievement, which is not surprising given the tales of his parentage, is his recognition as a truly great dancer. To this day dancers in India working in the classical traditions invoke him and pay him their respects. Patañjali, therefore, is effectively the patron saint of dance.
Some say that Patañjali also wrote a treatise on ayurvedic medicine. Certainly, the texts in question focus on what could well have been Patañjali's main interests: the diagnosis of disease; the structure and function of the human body; the problem of keeping the body fit, pleasing-feeling and good looking; and the curative values and properties of drugs and the techniques required to administer them. All these are mentioned in the Yoga Sutras. But although a strong tradition does insist that the Patañjali who wrote the ayurvedic text is the self-same Patañjali who wrote the Yoga Sutras, scholars do not accept this as an established fact. But an argument that can be made against these scholarly types is that they are rather missing the point. Svayambhus—divine beings who bring about their own causeless existences, who are without karma, and who manifest themselves as evolved and highly spiritual beings for the betterment of humanity—are in no way obliged to respect historical facts.
The waters are further muddied when it comes to another great treatise attributed to Patañjali.
It is (almost!) beyond dispute that a famous man named Patañjali was born in Gonarda and that he lived, for at least a little while, in Kashmir. This particular Patañjali lived and wrote in about (?!) 140 BCE. He was a great grammarian and his Mahabhashya or Great Commentary on Panini's grammar (the first great grammar written for any language) was magisterial. It is still read and acknowledged today. But the Mahabhashya was a lot more than just a commentary. The Patañjali who wrote it took Panini's work a great deal further. He redefined the rules of Sanskrit grammar. He greatly enlarged its vocabulary. He gave Sanskrit a muscular power that made it a more precise, subtle, effective and artistic instrument capable of expressing any aspect whatever of human thought or existence. Furthermore, this Patañjali did not just provide a body of theory. He demonstrated the possibilities of Sanskrit through his skills and artistry in its use.
Clearly, the question of the moment is whether the Patañjali who wrote the Mahabhashya was (a) the same as the Patañjali who wrote on ayurveda; and/or (b) the same as the Patañjali who wrote on yoga (never mind (c) the same as the one who was a founding father of dance).
Focusing on grammar and yoga, there is the inevitable initial problem of validating the necessary contemporaneous dates and locations. Although it is not conclusive, the best evidence is in the negative. The Patañjali of the Yoga Sutras surely lived several centuries before the Patañjali of the Mahabhashya. There is not (as) much leeway in the dates for the latter. Added to this is some internal evidence. Philosophical contradictions between the two texts would seem to indicate that they simply cannot have had the same author. This, however, is a far from convincing argument. It is easy enough, after all, to find writers who express contradictory ideas on the same page never mind in such different books, on such vastly different subjects, and written at different points in their lives. Furthermore, a work of grammar is a very different animal from a book on yoga. It is surely not to be wondered at, then, if ideas that show themselves to best advantage in the one field are not in any way efficacious—and, indeed, cause great difficulties—when carried over to another. The point is surely that both are excellent self-contained works with impeccable arguments and logical structures in their respective fields. This is surely exactly what they should be. It is true that it would be neat if it were otherwise but, at the end of the day, there is no reason why the one work is obliged to make reference to, or be 100% compatible with, the other.
All told, the tradition that conflates these three Patañjalis (four if dance is added to grammar, medicine and yoga) into one has been around some two millennia ... and it is not about to die out any time soon.