Final answer:
Plato held that the soul pre-exists before birth and is immortal after death, presenting arguments in the Phaedo based on his Theory of the Ideal Forms and the process of recollection. While not accepted by modern standards, his views on the soul and knowledge have been influential in the history of thought.
Step-by-step explanation:
Plato believed in the pre-existence and immortality of the soul. According to him, the soul exists apart from the body both before birth and after death. Plato, in dialogues such as the Phaedo, offered various arguments for the soul's immortality, which are based on his Theory of the Ideal Forms. These arguments, though not convincing to modern thinkers, posit that knowledge is a form of recollection from when the soul resided in the realm of pure thought, implying that the soul had a life before inhabiting the physical body.
The process of acquiring knowledge, for Plato, involves recollecting the eternal forms or ideas that the soul has been in contact with prior to its union with the body. This concept is framed within his larger philosophical system, where he delineates the material world as a shadow of the true world of ideas. Plato considered the soul's independent ability to engage in pure thought as evidence of its separateness from the body. Despite the rejected premises of today's understanding, Plato is credited as the first to attempt to provide a reasoned proof for the existence and immortality of the soul and for knowledge being innate and pre-existent.