Isaac Newton did a great deal to advance human understanding, including inventing a whole system of mathematics that we call calculus. His most famous achievement, however, is his discovery of the law of gravity, which changed the way scientists understood the universe. A famous quotation about Newton comes from the brilliant English Renaissance man Alexander Pope: "Nature, and nature's laws, lay bathed in night. God said 'Let there be Newton!' And all was light."

Whilst John Locke believed in liberalism and constitutionalism and limiting the power of absolute monarchs, Hobbes argued that absolutism was the only way to protect society from slipping into an anarchistic state of nature in which crime and chaos would reign. 

Leviathan is a seminal work of the Enlightenment period that stood in contrast to the writings of John Locke, Rousseau, and others. In Leviathan, Thomas Hobbes presents his arguments in favor of absolutism as a means of preventing society from descending into catastrophic anarchy. Hobbes argued in support of the absolute power of government to control mankind's base nature.

Voltaire was a French philosopher during the Enlightenment era who advocated fiercely for the protection of freedom of speech. Freedom of speech, according to Voltaire, is the best and perhaps only way to guard against the tyranny of government.

Descartes is an Englightenment-era philosopher, scientist, and mathematician, and his work in all three fields continues to be hugely influential today. He is famous for his reductive inquiry into the nature of existence that led him to one simple truth: "I think, therefore I am." Essentially, by doubting his existence, he was proving his existence, for for there to be doubt there must be something to do the doubting.

Montesquieu is a famous Enlightenment philosopher who wrote in his seminal work The Spirit of Laws that, to protect against tyranny, a democratic government should be divided into separate branches: an executive branch to enforce the laws, a legislative branch to pass the laws, and a judicial branch to challenge the laws.

Enlightened despotism (also called enlightened absolutism) was a form of absolute monarchy that existed in the eighteenth and early nineteenth centuries. The rulers, or enlightened despots, were heavily influenced by the ideas and theories spread by the Enlightenment thinkers of the time, particularly ideas concerning rationalism, freedom, and sponsorship of the arts and sciences. Of the European leaders listed in the answer choices, only Catherine the Great was considered an enlightened despot.

Mendeleev is most famous for his work in "perfecting" the periodic table of elements. His work allowed people to understand similarities and differences between chemical elements with greater clarity. The theory of relativity was an idea of Albert Einstein's, and Newton invented the system of calculus. Alchemy, the practice of trying to turn materials into precious metals, was very popular during the Scientific Revolution.

Although slightly less revered in popular history, the Northern Renaissance was no less significant or accomplished than the Italian Renaissance. Albrecht Durer is probably the most famous of the Northern Renaissance artists. He is renowned for his woodcuts and his watercolors, as well as his theoretical writings on mathematics and perspective. 

Isaac Newton and Gottfried Leibniz are two prominent Enlightenment Era scientists and mathematicians. Seemingly they both independently devised a system of calculus that allowed them to make calculations on things previously impossible. It is generally accepted that Newton invented calculus first, but as he did not publish this information for decades scholars have to rely on clues in his publications and on Newton's word (notoriously unreliable). The two men battled for acclaim for the invention during their lifetimes, but it is Newton who is most commonly remembered as the inventor of calculus (at least in the English speaking world), despite the fact that Leibniz was the first to publish on the matter. Calculus was vital to some of the scientific breakthroughs of Newton's lifetime and has been continued to be ever since.