Oxford Reference – Yetzer Ha-Tov and Yetzer Ha-Ra:
The good inclination and the evil inclination.
In the typical Rabbinic doctrine, with far-reaching consequences in Jewish religious thought, every human being has two inclinations or instincts, one pulling upwards, the other downwards.
These are the ‘good inclination’—yetzer ha-tov—and the ‘evil inclination’—yetzer ha-ra.
The ‘evil inclination’ is frequently identified in the Rabbinic literature and elsewhere with the sex instinct but the term also denotes physical appetites in general, aggressive emotions, and unbridled ambition.
Although it is called the ‘evil inclination’, because it can easily lead to wrongdoing, it really denotes more the propensity towards evil rather than something evil in itself. Indeed, in the Rabbinic scheme, the ‘evil inclination’ provides human life with its driving power and as such is essential to human life.
It is not too far-fetched to read into this homily the idea that life without the driving force of the ‘evil inclination’ would no doubt still be good but it would be a colourless, uncreative, pallid kind of good. That which makes life ‘very good’ is the human capacity to struggle against the environment and this is impossible without egotistic as well as altruistic, aggressive as well as peaceful, instincts.
The Rabbinic view is, then, realistic. Human beings are engaged in a constant struggle against their propensity for evil but if they so desire they can keep it under control. The means of control are provided by the Torah and the precepts.
One of the most remarkable Rabbinic passages in this connection states that the Torah is the antidote to the poison of the ‘evil inclination’ (Kiddushin 30b). The meaning appears to be that when the Torah is studied and when there is submission to its discipline, morbid guilt-feelings are banished and life is no longer clouded by the fear that the ‘evil inclination’ will bring about one’s ruination.