"Restatement on Xenophon's Hiero," What Is Political Philosophy?  The Free Press, 1959.  Reprinted in On Tyranny.

Excerpt:

A social science that cannot speak of tyranny with the same confidence with which medicine speaks, for example, of cancer, cannot understand social phenomena as what they are.  It is therefore not scientific.  Present day social science finds itself in this condition.  If it is true that present day social science is the inevitable result of modern social science and of modern philosophy, one is forced to think of the restoration of classical social science.  Once w have learned again from the classics what tyranny is, we shall be enabled and compelled to diagnose as tyrannies a number of contemporary regimes which appear in the guise of dictatorships.  This diagnosis can only be the first step toward an exact analysis of present day tyranny, for present day tyranny is fundamentally different from the tyranny analyzed by the classics.

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