Plato - souls is distinct from the body and is capable of maintaining a separate existence. This is called dualism - body and souls 2 different things , implication that after death the soul is able to continue, it is IMMORTAL.
Plato believed that a human has 3 distinct parts - mind, body, soul. Body is in state of change and can't truly reflect the form of man. Soul however is immortal and unchanging. Body is our physical form, can be touched and seen, but we are separate from the bodies that we inhabit. The mind can become aware of eternal truths beyond the physical world. For Plato, the mind and body are in opposition - body desires food and sex etc. while the mind seeks knowledge and understanding of the world.
The souls for Plato, is the directing force of the body. It lasts us see the true knowledge, it is never confused. Plato believes that death separates the soul from the body. Therefore Plato believes in the IMMORTALITY OF THE SOUL because the soul lives on after the death of the body.