There have been many theories made about the human soul by philosophers in ancient Greek history. Two of the most influential and infamous philosophers in ancient Greece were Plato and Aristotle. Both Plato and Aristotle did, in fact, believe in a soul for all living things. They also both believed that the soul did not exist in humans alone.
Although Aristotle studied under Plato as his student, he possessed slightly different ideas about the soul, aside from the actual belief in the soul itself, and within whom and what it exists. While Plato's outlook was more unworldly, Aristotle looked to nature, especially through biology, for many of the answers to his queries. These philosophers had opposing views on whether or not the soul was separate from the body. They also disagreed on the immortality of the soul. Plato was a dualist, meaning that he believed that the body was separate from the soul. He viewed the soul as an entity, rather than a life force.
He also believe that since the soul was not material and only material things may dissolute, that the soul was immortal. Plato also believe that the soul exists far before birth and long after death. Aristotle on the other hand, believed that the soul and the body are one and cannot exist without the other. This idea also works for the concept of sight; "when sight is removed, the eye is no longer an eye except in name, no more than an eye of a painting or a statue." Similarly, if the eye were an animal, sight would have been it's soul. He argues that the soul is the life force rather than the entity. He felt that the soul is the principal of existence in this world and enters the body at birth.
"The soul and body can be distinguished only in thought, not in fact." Since the soul is the main ingredient for life, it is inseparable from the body. If it is indeed inseparable from the body, it would only follow that when the body dies, with it goes the soul, therefore the soul is not immortal. If the soul is not immortal, it is impossible for it to go on after death, for that reason, no, Aristotle does not believe in life after death. (Although he does go on to say that the "rational soul" may be able to exist apart from a body. ) As stated in the introductory paragraph, both Plato and Aristotle believe that the soul was not limited to humans and that it contained three types or parts. Plato was a supporter of reincarnation, where the soul goes from one being to the next (animals included) until the soul is truly purified.
In the Republic, Plato gave his theory that the soul was made up of three parts: reason, emotion and desire. Aristotle, like Plato, believed that all plants, animals and humans possessed souls, however, he did not trust that a soul may go on from one species to the next after death. He believed that each species had different levels of soul. He too had a theory on different parts of the soul, but contrary to Plato's view, he felt that the different parts were actually different souls or types of souls altogether.
These souls consisted of the nutritive soul, the sensitive soul, and the rational soul. The nutritive soul, which is the efficient cause that initiates change and movement, is possessed by plants, animals, and humans and is the lowest form of soul. The sensitive soul, which is the final cause and the bodies goal, is the second highest form of soul and is possessed by animals and humans. The rational soul, which is the formal cause and the organizing cause is the highest form of soul and is possessed by humans alone.
This rational soul, as discussed by Aristotle, may be able to survive worldly death, and continue on into a higher existence. Both philosophers, Plato and Aristotle has interesting theories on the concept of the soul. Plato took a more psychic and spiritual approach in his theories, while Aristotle chose to be more scientific while employing elements of biology and metaphysics, using concepts of substance, form and matter. In fact, there is a famous Renaissance fresco in the Vatican, painted by Raphael, that shows Plato walking with his student Aristotle.
Plato is pointing to the heavens and Aristotle is pointing to the ground. Although I respect and appreciate the contributions that each philosopher has made to modern day philosophy, I feel that Aristotle's beliefs more closely resemble my own, than those of Plato. I tend to accept scientific ideas over abstract ones and therefore, relate to Aristotle. I also found that Aristotle's concepts were better organized and much easier to read and truly understand.
Aristotle's scientific approach convinced me of a human soul, which is something that, prior to reading his writings, I had not believed in. Aristotle not only provided me with new ways to contemplate the idea of a soul, but he gave me a whole new view on the soul as an actual, existing part of myself.