The soul is referred to by a number of names, each one corresponding to one of its different functions. The five ways of referring to the soul are nefesh, ruah, neshama, haya, and yehida. The first three names refer to those aspects of the soul corresponding in turn to: our desires and drives (nefesh), our anger and emotions (ruach), and our mental understanding (neshama). The other names, haya (alive) and yehida (unique), correspond to the aspects of the soul which are eternal and incomparable to any other creation.

The meaning of the names nefesh, ruah, and neshama:

The soul only functions together with the body, for, in order to function, every creation requires the means with which to act. When the soul is connected to the body [during a person’s lifetime], three of its properties are evident: cognition, anger, and desire. This is why we have three different names for the soul: nefesh, ruah, and neshama. The name nefesh indicates that the soul has desires…. The name ruah indicates that it can become angry…. The name neshama indicates its intellectual abilities.

The meaning of the names haya and yehida:

The terminology relating to the soul includes two additional names: haya and yehida. It is called haya because the Creator gave it eternal life. The name yehida indicates that this aspect of the soul is unique in the universe. (Rav Se’adya Gaon, Emunot VeDeot 6)

Even though a person has only one soul, that soul has a number of components and different faculties. Just as a doctor who wants to heal a person’s body must know the different parts of human anatomy, so too, in order to heal a person’s soul and help him improve his character one must be familiar with its different components. The soul has five components: (1) the nutritive component that maintains the body and is responsible for everything connected with nutrition and growth; (2) the sensory component, responsible for the five senses; (3) the imaginative component, responsible for everything connected with memory and imagination; (4) the emotional component, connected with drives and will; (5) the intellectual component.

These are the components of the soul: (1) The nutritive component is the source of the ability for ingestion, retention, digestion, excretion, growth, reproduction, and separating between fluids that are important for nutrition and those that are to be expelled…. (2) The sensory component is responsible for the well-known senses: sight, hearing, taste, smell, and touch. This component is present throughout the body…. (3) The imaginative component is the ability to remember sensory impressions even when no longer experiencing the sensation. It can connect some sensations and disassociate others. This imaginative component can also connect certain ideas which a person has experienced to ideas which he has not experienced at all, and even those which cannot be experienced, such as where a person might imagine a ship made of iron sailing through the air.… (4) The emotional component is the faculty whereby a person either desires something or is repelled by it. This drives a person to either seek something or avoid it, to choose it or reject it. [It is the source of] anger and desire, fear and strength, cruelty and mercy, love and hate, as well as many other similar emotions and character traits. This faculty expresses itself through all the body’s limbs. (5) Man’s intellectual component is the faculty with which he understands and where his insight lies. Through it he acquires wisdom and distinguishes between appropriate and inappropriate actions. (Rambam, Shemoneh Perakim, chap. 1)