PSYCHE is ‘rational soul’. This ancient Greek term also indicates ‘spirit’, ‘self’, ‘life’, ‘conscience’, ‘living principle’. The equivalent Latin term in Lucius Annaeus Seneca (Seneca the Younger) is <animus>, the intelligent soul.
Stoics are materialists so, for them, the soul itself has substance. However, in origin, the notion of <psyche> is in relation to breath (<pneuma>). Indeed, in its earliest usage (Homer) <psyche> is a breath-like material persisting after death as a mere ghost. The use of <psyche> as a reference for the location of thought and emotion only begins under the influence of philosophy. It is in the fourth century BC that it becomes normal to pair and contrast <psyche> with <soma>(body).
For Stoics the <psyche> features different degrees corresponding to various states of consciousness. For instance, a dead man is someone who has entirely lost his <psyche>. Instead, a sleeping or fainting man has only lost enough of his <psyche> in order to lose consciousness.
<Psyche> is ‘rational soul’. It means that in ancient times any individual has more than one soul. Or it means that the soul has different parts, one being rational and another being irrational. As a matter of fact, in modern psychology (term deriving precisely from the Greek word <psyche>) the psyche always has different components. For instance, see Sigmund Freud‘s structural model of the psyche and its division in ‘id’, ‘ego’ and ‘superego’. Freud’s earlier, topographical model of the mind divides the mind into the three elements of conscious, preconscious, and unconscious. The ‘conscious’ contains events that we are aware of, the ‘preconscious’ regards events that are in the process of becoming conscious, and the ‘unconscious’ includes events that we are not aware of.