Question:

I would like to know whether the "yetzer hara" or "evil inclination" is an equivalent term to "animal soul." I've seen these two terms used (seemingly interchangeably) in Jewish and chassidic literature to describe man's base desires.

If they're not the same, what is the relation between the two?

Answer:

That's an interesting question. Although the two terms sound similar and are often interchangeable, they refer to two different things.

Your animal soul, the nefesh habehamit, is the source of all your self serving – but not necessarily evil – drives. In one word, the animal soul is self-centered passion. That doesn't mean it is bad. It can be neutral, or even good.

The yetzer hara is one's evil inclination. Think about what that means: your inclination to do evil. For example, the desire to eat non-kosher food, steal money, or do anything forbidden by the Torah. Those are all products of the yetzer hara.

The word yetzer is related to the Hebrew word tziyur, "form." In other words, the yetzer hara takes the raw material of the animal soul's benign passion and provides it form by channeling it towards immoral ends.

Thus the yetzer hara – the form of the animal passion – must be destroyed or at least ignored, since it is intrinsically evil. The animal soul, on the other hand – that raw passion – needs only to be re-formed and re-channeled. Generally, this needs to go step by step: Once the bad form of the yetzer hara is destroyed or weakened, then it becomes possible to provide the animal passion with a new, positive form.

The animal soul naturally gravitates towards that which it perceives as pleasurable and gratifying. As physical beings, our default pleasures are physical, and often of the forbidden variety. It is our task to reprogram the animal soul, to teach it that while it is fine to satisfy its selfish cravings—it should crave that which is infinitely better and sweeter than anything this world can offer—namely, a connection with G‑d.

If the animal soul can be successfully programmed to desire the divine, the practical benefit is great. For the force of the animal soul's fiery passion is far greater than the G‑dly soul's. Think for a moment about your excitement over a fine steak, as opposed to your "excitement" about doing a mitzvah. Can you imagine channeling that excitement and enthusiasm towards praying or giving charity?

Malkie Janowski for Chabad.org

Sources:
Likuttei Torah, Chukat 56c ff.; Hemshech 5672 vol. 1 p. 46. See also Torah Ohr, Miketz 38b ff. for an alternate (but similar) explanation as to the difference between the animal soul and the yetzer hara.