How is the supreme court able to check the power of congress?

The Supreme Court uses judicial review to declare actions by the President or Congress to be invalid if they are contrary to the Constitution. The Constitution is the supreme law of the land and no presidential act or congressional laws may conflict with it. The Courts are the interpreters of the laws and as such they interpret the Constitution and laws to decide if they conflict with one another.

Further, it allows the Judicial Branch to "define" that law by answering questions about it that are not spoken to directly in the regulation itself.

Chief Justice John Marshall clearly affirmed the power of judicial review in the case Marbury v. Madison, (1803), when the Court declared Section 13 of the Judicial Act of 1789 unconstitutional. It should be noted that the US Supreme Court, for the most part, determines what laws to review based on decisions made in lower Federal Courts. In most cases the Court waits for a case to be presented to them. It then can reject hearing the case or depend on the ruling of the lower courts.

social contract theory basically says that all individuals are born equal, and provided a god given right to consent to be governed. american government is based of this

thomas hobbes and john locke said that we are selfish, individualistic, and constantly at war with each other, therefore we need to be controlled. 

government is defined as the legitimate use of force to control human behavior within territorial boundaries, here comes in hobbes and locke.

hobbes takes the part about controlling human behavior. while locke takes the part of legitimate use of force, since force is not legitimate unless there is consent of the people. 

there are basically 3 goals of the government: 1) maintain order by protecting life and property. 2) providing public goods, those which are typically not provided by the public sector, such as roads and education. 3) promote equality be it political, opportunist or outcome equality. 

i'll write a docs for you. hold on for a moment