quoted from Alan Gewirth, Political Philosophy (Macmillan, 1965)
The central concern of political philosophy is the moral evaluation of political power. In its most important manifestation, political power is found in the state with its laws and government, which are formally and for the most part effectively supreme over all other rules, institutions, and persons in any society. Political philosophy deals with the criteria for bringing these supreme political controls under moral control by subjecting them to moral requirements concerning their sources, their limits, and their ends or purposes.
It follows from this that political philosophy is a branch or application of moral philosophy.
... The right way to put the relation between moral philosophy and political philosophy seems to me the following. Moral philosophy deals with the most general considerations of moral values and obligations, while political philosophy deals with the applications of these considerations to the moral questions of politics and the political order. (pp. 1 f.)
Basic Questions of Political Philosophy
the chief concern of political philosophy is with the most general moral questions of society and government, the questions whose answers are more or less directly decisive for all other questions of political morality.
What are these most general questions? We may list them schematically as falling on three major different levels, as follows:
1. General question about society: Why should men live in society at all?
2. General question about government: Why should men obey any government at all? Why should some men have political power over others?
3. Specific questions about government:
a. Source and locus of political power. By what criteria is it to be determined who should have political power?
b. Limits of political power. By what criteria is it to be determined what should be the extent of political power and what rights or freedoms should be exempt from political or legal control?
c. Ends of political power. To the attainment of what affirmative ends should political power be directed, and what are the criteria for determining this? (p.4)