The Founding Fathers believed in the republican form of government. A republic is a system of government where individuals elect representatives to speak for them in the government. They were skeptical of democracy, which is technically defined as direct involvement of the people in policy making.

John Locke is often considered the grandfather of the constitution. He wrote that people are endowed with natural rights of life, liberty, and property. Thomas Jefferson when drafting the Declaration of Independence, borrowed directly from these ideas when he wrote life, liberty, and the pursuit of happiness.

The Founding Fathers, highly educated and intellectually active men all, were influenced by several sociopolitical philosophers. Thomas Paine’s Common Sense (1776) was exceptionally popular; Paine directly addressed the budding feelings of Revolution amongst the colonists, passionately championing the struggle to throw off tyranny, regardless of how fierce the opposition. Many of the Founders, especially Thomas Jefferson, took inspiration from John Locke’s discussion of the many benefits of a limited government. Locke’s idea that individuals innately possessed certain natural rights (which can from birth, not the government, and therefore could never be removed), combined with his certainty that a government was only legitimate if it received the consent of those it governed, are quite clearly echoed within the Declaration of Independence itself. The Founders were also greatly influenced by the Baron de Montesquieu, a French nobleman whose free-thinking notions belied his privileged station. In his many writings, the Baron set forth the idea of separate branches of government, each able to check the actions of the other. While the Founders were indeed aware of the theories espoused by Thomas Hobbes, they tended to disagree with most of the philosopher’s statements, especially his fervent love for monarchies and absolute rulers.

John Locke, as an advocate for limited government, believed that a government’s most essential and vital purpose was the protection of the natural rights of its citizens. According to Locke, natural rights are automatically endowed upon every person at birth, as an innate human quality, much like the human needs for shelter, food, water, and air. Natural rights are intrinsic and irrevocable and therefore cannot be taken away by any governmental power. The most important of these natural rights include life, liberty, and the protection of private property, all of which are woven in together to constitute the entire spectrum of natural rights. According to Locke, any politically moral and socially responsible government must take as its first and most basic responsibility the protection of these natural rights, from which all other benefits (such as the safeguarding of a strong economy and the national security) will then follow.

James Madison, echoing the writings of Aristotle, argued that the most enduring divisions within society are between the rich and the poor. Therefore, mixed systems are best to govern and to balance these factions.

McCulloch v. Maryland was the first constitutional case in 1803 to deal with interpreting exactly what powers rested with the national government. The Necessary and Proper clause was interpreted to give the national government implied powers beyond those powers explicitly stated.

While all of the answers were influential Enlightenment philosophers, only Hobbes wrote "The Leviathan" in 1651, which was very influential when the Framers were writing the Constitution. Rousseau wrote "The Social Contract". Locke came up with the idea of "natural rights" which influenced Jefferson when he was writing the Declaration of Independence. Montesquieu wrote about the separation of powers in government. 

Rousseau's idea of the "social contract," which asserted that the people must give up some freedom to gain the protection of the government, heavily influenced the Constitutional Framers. Although both Locke and Hobbes were important Enlightenment thinkers, neither wrote about the "social contract." Socrates was a Greek philosopher, not and Enlightenment Philosopher. Montesquieu wrote about the separation of powers in government.