The framers of the Constitution came together to make sure they made the best government possible. On one hand, they did not want they people to have much power and they did not want any one person in the government to have all the power. For this to work, they decided to split the government into three different branches. The executive power would enforce the laws and would be exercised by on single person. The legislative power would make the laws. This would be done by an assembly with two chambers: the upper chamber, consisting of the aristocracy and the lower chamber chosen by the people. The third branch, the judicial power, the application of law to particular situations exercised by independent judges. .
All of this came from an Englishman in the 1600's named John Locke. He said "that a country's founder should create a separation of powers for their government," or a system of government in which different institutions exercise various components of governmental power. Locke came up with the first two powers, the legislative and executive, but the judicial power was thought up by a French philosopher Charles de Secondat sixty years after the writings of Locke.
After the Articles of Confederation, the framers wanted to improve on its weakness, like the congress not being able to levy taxes. In Article 1, section 8, it gave congress power to do so. The executive branch was not independent from congress in the Articles of Confederation. In Article 2, an independently elected president holds the executive power. Anther weakness of the articles was that their was no national judicial system. Under Article 3, section 1, the Supreme Court was created and the Congress was granted the power to establish lower federal courts. .
The delegates first made the necessary and proper clause, which said that Congress has the power to "make all laws which shall be necessary and proper for carrying into execution.