Mathematics, abstract reasoning, and experimentation all provided tools for studying the natural world in the seventeenth century, and they also provided tools for thinkers contemplating the place of humans and God in that world, and the limits of human knowledge. Descartes based all knowledge on our intuition about God’s existence and understanding of ourselves as thinking beings, but other philosophers had different ideas. Baruch Spinoza (1632–77) was born to Jewish parents in Amsterdam, but his freethinking and unorthodox views led him to be thrown out of the Jewish community. He traveled from town to town, making a living as a lens-grinder, an occupation that cut his life short because he steadily breathed in glass dust. Hostility to his earliest published works and political instability in the Netherlands led him to withhold his writings from publication, and his main work, Ethics , was only published after he died. In Ethics (1677), Spinoza argues that there is really only one substance in the universe. That substance is God. God and Nature, Creator and creation, mind and matter are all the same, a position called pantheism, which Spinoza demonstrated through logical geometrical proofs and theorems. Our sense of remoteness from one another or separation from God is an illusion, he asserted, and our immortality is certain, as the One Substance is eternal. Whatever happens is destined to happen – a position called determinism, akin to Calvin’s idea of predestination – but because God and the universe are one, we can be confi dent that things happen for a reason. We do not have free will, but if we understand our place in nature, we can achieve freedom of mind and an intellectual love of God, a state Spinoza calls bliss. This bliss, this sense of oneness with God and other people, is vastly superior to any other emotion, which Spinoza urges us to control. The German philosopher Gottfried Wilhelm Leibniz met Spinoza, and built his own philosophical system on Spinoza’s ideas, though their lives were dramatically different. In his long life, Leibniz corresponded and visited with thinkers, rulers, and statesmen all over Europe, serving as a diplomat in Paris and the offi cial historian and librarian for the dukes of Brunswick. He invented the calculus independently of Newton, and sought to apply Cartesian rational principles to law, theology, and politics as well as scientifi c issues. He was fascinated by Chinese learning, corresponding with Jesuits who had been in China and writing a knowledgeable book praising Chinese culture. Leibniz accepted Spinoza’s notion that everything happens for a reason, and because all reasons are God’s and God is good, everything must happen for a good reason. The world as it exists is only one of many possible worlds, but because it is what God has chosen, it is the best of all possible worlds. Suffering and evil are the result of our not understanding God’s reasons. Leibniz was ruthlessly satirized in the French author Voltaire’s anonymous novel Candide or Optimism (1759) in which the young hero Candide, accompanied by his Leibniz-quoting tutor Pangloss, experiences a series of dreadful events, including shipwrecks, trials by the Inquisition, starvation, fl ogging, and the Lisbon earthquake of 1755, which was followed by a tsunami and fi re. No matter what happened, Pangloss responds with “everything is for the best in this best of all possible worlds,” until fi nally by the end Candide decides that simple work is the only real escape. “All that is very well,” he says in the last words of the book, “but let us cultivate our garden.” While Descartes, Spinoza, and Leibniz viewed abstract reason as the best tool for understanding the world, the English philosopher and political theorist John Locke (1632–1704) picked up on Francis Bacon’s emphasis on experience, observation, and sense perceptions as the true basis of knowledge. In An Essay Concerning Human Understanding (1690) Locke argued that the mind at birth is a blank tablet ( tabula rasa ) with no innate ideas. All knowledge is derived from actual experiences, a position called empiricism or experientialism; education was thus extremely important, for only through education could the mind reach its fullest potential. Locke’s empiricism was not absolute, however, for he did make room for both reason and faith in the acquisition of knowledge. Reason, experience, and divine will were not only the sources of human understanding for Locke, but also the proper bases for government. In Two Treatises on Government (1690), Locke challenged both Robert Filmer (1588–1653), whose Patriarcha based the divine right of kings on the patriarchal power given to Adam by God, and Hobbes, who viewed the original “contract” by which monarchs had been given authority in return for order as immutable. Locke did not see the family and political society as analogous; property, not fatherhood, was the proper basis of political authority. God had given the world to humans in common, and individual property derived from applying labor and talents to that common inheritance; the state of nature was not, as it was for Hobbes, “solitary, poor, nasty, brutish and short,” but rather pleasant. Individuals had not formed a contract with governments to avoid chaos, but simply to better assure protection for their property. Monarchs who did not do this, or who applied their powers in capricious or arbitrary ways, could justifi ably be overthrown. Locke uses the word “property” in several senses. Narrowly, he takes it to mean land, goods, and money. Only those who owned property, he argued, could be free enough to make political decisions without being infl uenced by others, an idea that fi tted well with the political realities of England in the late seventeenth century, and provided justifi cation for limiting voting rights in national elections to property-owning males until the nineteenth century. (In a few local elections in some areas of Britain and eventually in some British colonies in North America, unmarried and widowed female property owners were allowed to vote. Laws that eliminated property ownership as a requirement for voting in the nineteenth century used the word “male,” thus explicitly excluding women on the basis of their gender.) More broadly, Locke uses property to mean “life, liberty, and estate,” which he describes, somewhat vaguely, as “natural rights” given to humans by God. Tyrannical monarchs could thus be legitimately opposed when they failed to protect individuals’ property, but also when they failed to uphold these broader natural rights.