In Judaism, yetzer hara (Hebrew: ??? ???? for the definite "the evil inclination"), or yetzer ra (Hebrew: ??? ??? for the indefinite "an evil inclination") refers to the inclination to do evil, by violating the will of God. The term is drawn from the phrase "the imagination of the heart of man [is] evil" (Hebrew: ????? ??? ??????? ???,yetzer lev-ha-adam ra), which occurs twice in the Hebrew Bible, at Genesis 6:5 and 8:21.
The yetzer hara is not a demonic force, but rather man's misuse of things the physical body needs to survive. Thus, the need for food becomes gluttony due to the yetzer hara. The need for procreation becomes sexual abuse, and so on. The idea that humans are born with a yetzer ra (physical needs that can become "evil"), but that humans don't acquire a yetzer tov ("a good inclination") until an age of maturity—12 for girls and 13 for boys—has its source in Chapter 16 of the Talmudic tractate Avot de-Rabbi Natan.
Traditionally, a person's indulgence of either the good or evil impulse is seen as a matter of free choice. For example, Moshe Chaim Luzzatto, wrote in Derech Hashem ("The Way of God") that "Man is the creature created for the purpose of being drawn close to God. He is placed between perfection and deficiency, with the power to earn perfection. Man must earn this perfection, however, through his own free will...Man's inclinations are therefore balanced between good (Yetzer HaTov) and evil (Yetzer HaRa), and he is not compelled toward either of them. He has the power of choice and is able to choose either side knowingly and willingly..."[1]
