Abstract: The intention of this paper is to show how Leo Straussʼ mature writings respond to the twofold necessity of political philosophy: contributing, at the same time, to the good of the city and to the good of the philosophers. In the first place, it will try to prove this point by analyzing in detail the Introduction to On Tyranny (1948), which represents an essential step in order to understand the intention of the author. In the second place, it will tackle the problem of justice, that is, of natural right, by concentrating on the so called “tyrannical teaching”. This teaching is a way to present a truth which the city cannot find acceptable, that is, an unpleasant truth concerning the irresoluble problem of justice and legitimacy. In conclusion, it will point to the tension between philosophy, i.e., search for knowledge, and the city, i.e., the realm of opinion. For the philosopher, as such, has to “corrupt” the young in order to pursue his search for knowledge of the whole, or the nature of all things. Therefore, he weakens the city, since philosophizing implies unbelief in the gods of the city.