Political science is as it says - the academic field concerned with the study of politics. The "science" part is a remnant of nineteenth century positivism and optimistic beliefs in the powers of human understanding - for if man could understand the natural sciences as completely as he appeared to at the turn of the century, surely he could understand himself by stringent applications of the same methods? Political science is yet to furnish us with absolute laws of human political behaviour, but as a by-product of this "failure" it has produced a huge amount of literature which enriches our knowledge of the world and ourselves.
Early "political philosophy" was mainly concerned with ideals - how the ideal Commonwealth might be established and maintained, how society could be structured to maximise the Good, and what rights, freedoms and duties were applicable to the Commonwealth. Political science tends to distinguish itself as the study of what is, not what "should" be - and as such it is considered part of the social sciences. Its relationship with the other social sciences is an interesting one - some see it as their lackey, because it is said to rely on them for its theories and the "meat" of its analysis. Others say it is the central social science because human political institutions are a part of all the others, and an understanding of them is essential to understanding the other social sciences. International Relations, for instance, tended to be seen as a part of jurisprudence, economics and sociology, but after World War II it developed into a distinct field of its own under the umbrella of political science (after the second unsuccessful attempt by man to commit suicide, scholars were understandably concerned with how this might be avoided in the future).
The relation of the political scientist to the system he studies is particularly interesting because he himself impacts on that system - when he writes, people understandably pay attention. This means he impacts the decision-making process and the thoughts of important actors in the process, from journalists to lobbyists to elected officials. The relationship between the two fields of political science and history is also interesting - scholars that are equally at home in both fields might write a book and leave the reader wondering whether he just read a history book or a political science book. Political scientists are naturally interested in the events of the past to aid them in their analysis and understanding of what might happen in the future, although becuse history does not repeat itself they cannot be expected to succeed in this as the positivists once claimed they would. For instance, Western political science completely failed to predict the collapse of the Soviet Union in 1989. Political scientists still generalise much more than historians and try to extract general "rules" - something many people consider it is the historian's duty to avoid.
When political science delimited itself in its own field, it was largely separated from economics. Prior to the 1870s scholars and philosophers tended to refer to "political economy", a name which implicitly rules out the possibility of free-market libertarianism. People who opposed the liberal tradition in economics such as Karl Marx (who denied the distinction between politics and economics existed) continued to refer to "political economy", but nowadays the term is largely defunct. This does not mean that Western scholarship has accepted economic liberalism as its guiding theory (quite the opposite), it just means the two fields have become more professional and exclusive within their own areas. Many liberal economists referred to "political economy" in the nineteenth century and today many statists refer to "economics".
Political science is often an applied instance of game theory. Nowadays it concerns itself with the study of everything from dog licencing to diplomacy, and the debate over what exactly can be discovered by the field and what cannot (as well as what should be studied) still rages. A strong scientific tradition dominates the study of public policy, in which scholars try to derive objective laws about what policies would and would not work in particular situations. People who advocate that political science has a strong scientific basis with objective laws that can be discovered, are part of the movement usually called "behaviouralism".
Some theories of state