Following Aristotle, many in the West had theorized that the matter had to be prepared to a certain point before this could happen and, prior to then, there was only a vegetative or sensitive soul, but not a human soul.

These three are assigned to the vegetative soul.

Thus, plants have "vegetative souls," animals have "sensitive souls," while human beings alone have "intellectual" - rational and immortal - souls.

Who is there of that school that is not persuaded that substantial forms, vegetative souls, abhorrence of a vacuum, intentional species, &c., are something real?

"Aristotle talked of the vegetative soul, which is basically equivalent to life at the cellular level," said Dr. Lee M. Silver, a professor of molecular biology and public affairs at Princeton.

He cites the Zuozhuan (534 BCE, see below) using the lunar jishengpo 既生魄 to mean "With the first development of a fetus grows the vegetative soul".

The difference between them is simply the essence of life or its vegetative soul.

He thought that according to Aristotelian principles, the vegetative and sensitive souls were of different substance than the intellective soul.

In this work, he differed from Aristotle in arguing that, in addition to a male seed, there is also a female seed, which contributes the vegetative soul to a fetus.

In On the Generation of Animals he declared that the soul develops first a vegetative soul, then animal, and finally human, adding that abortions were permissible early in pregnancy, before certain biological processes began.