16th and 17th century Europe
The Greek philosopher Aristotle, rehabilitated during the Renaissance, was often wrong in his assumptions concerning natural science. He maintained that fossils were either the skeletons of dragons or imprints from the heavens such as fallen stars. If his diagnosis was sometimes off-base he was responsible for inspiring a serious classification of species. Aristotle’s rational view of the world is the base for modern science and philosophy.
The Polish astronomer Nicolaus Copernicus (born 1473) came to the conclusion that it was impossible for the earth to be the epicenter of the universe. Scientists in the 15th century were hindered by the ever-present Inquisition which had banned the study of the planet, and fearing the discovery would cause him trouble he put off making his thesis public. His work was published the year he died, in 1543.
The theory presented by Copernicus was damaging to the Catholic Church, whose doctrine dictated that God made man and His world the center of all things.

With the invention of the telescope Galileo Galilei (born 1564) confirmed Copernicus’ theory. He was arrested by the Inquisition after claiming that the earth rotated around the sun and on its own axis. To avoid torture and a life sentence Galileo recanted and signed a document promising never to bring the subject up again.
“Eppur, e` vero.”

After he signed a retraction for the Inquisition
Galileo is alleged to have said said,
“Nonetheless, it’s true.”
Francis Bacon (born 1561) helped Galileo with his studies on optics and refraction. He figured the only way to make a correct analysis was through induction, or probable cause.

Bacon was a philosopher, a jurist, an alchemist and an astronomer, spoke several languages and studied the Arab scholars. He approved the philosophy of the Atomists and admired Aristotle. He felt that studies had deviated from the true objective of philosophy and science which was to research the relationship between humans and their world. Bacon is known as the father of Empiricism, a movement based on the the senses rather than pure deductive logic as the source of knowledge (the truth).

Though he did not win any particular favors with Queen Elisabeth, he was knighted and held several court positions, including attorney general under her predecessor King James. In 1621 he was imprisoned for accepting bribes. When he returned to Oxford he wrote, amongst other works, a compendium on theology that was published just before his death in 1626. He died of pneumonia after his research on the effects of freezing meat.

Thomas Hobbs (born 1588) was friends with Galileo and Bacon, and revived the materialist approach of the pre-socratic philosophers Anaxagoras and Empedocles, where everything is matter. He lived during the reign of Queen Elisabeth in a period of religious turmoil and his views caused his life to be threatened and his works to be banned. With all this he lived to defend his theory until he was ninety-one.

René Descartes (born 1596) was educated in philosophy and mathematics by the Jesuits in Paris and received a degree in law. His analytical approach to his studies had him doubting everything he learned and he enlisted as a soldier to find out more about the human condition. Though he never saw a battle it allowed him to observe other European cultures. He retired twenty years in Holland where he arrived at a major, irrefutable truth. Using the mathematical laws of deduction to solve a philosophical dilemma he came up with a certainty: we think. No matter what we think, even if it’s wrong or in a dream: we’re thinking. This cannot be denied, which inspired his statement: “I think therefore I am” (Cogito ergo sum.) His theories are called "cartesian". Descartes’ best known writings are the Discourse on Method and Meditations, published in 1641.

Blaise Pascal (born 1623) was a child prodigy in mathematics. He later embraced the idea of predestination and faith as the only road to salvation and entered Jansenist order, an orthodox sect of the Catholic Church that strictly followed the teaching of Saint Augustine. 

Baruch Spinoza (born 1632) was the only prevalent Jewish philosopher of his times but because of his controversial views was expelled from the Jewish community (who had migrated to Amsterdam during the period of the Inquisition in Spain and Portugal.) He was educated as an orthodox Jew and spoke several languages including ancient Greek and Latin. Latin was the written language used by scholars in Europe, who were all Christians. Spinoza refused a position as professor of philosophy to continue his work unhindered and earned his living polishing glass for lenses and telescopes. He lived alone dedicated to his studies (and to translating the Bible into Dutch) but corresponded extensively with other philosophers.

Spinoza was also interested in science and politics (he believed that to maintain order it was necessary to have freedom of speech) and was an accomplished mathematician. He used Descartes’ method of deductive reasoning to arrive to his conclusions. On the other hand he was opposed to the Cartesian concept of duality.

Spinoza did not separate the mind and the body as individual elements, as did the Cartesians, but considered them as a part of the whole. He concluded that this force, or God, must exist and not just in some other world but everywhere and in everything. His idea of self-realization is similar to Plato’s cavern theory. We are not aware of the causes that determine our actions (facing a wall with only shadows as guides.) Only through reflection and insight can we be liberated (reach towards the light) and come to terms with life (freed of our chains.) If we look at the global picture our personal problems seem minute and with this perspective we can live in harmony or “see life through the eyes of eternity” (sub specie aeternitates.) His book Ethics was published before his death but most of his works were printed posthumously.

Godfried Wilhelm Leibniz (born 1646), German mathematician and philosopher, turned down a professorship in philosophy when he was twenty one. His degrees were in science, law, diplomacy and logic, and he was historian for King George of England. His conclusions on cause and effect are reminiscent of the early Atomists, who believed the universe was made of substances that had a specific role, or purpose. Leibniz called these substances monads, dots in the universe that exist in synchronized accord or, in his words, “pre-established harmony.” Leibniz saw motion as an integral part of matter. Activity is generated not by matter itself (which is material) but through the energy produced by motion. However in this perfect world there is also free will and its imperfections.

John Locke (born 1632) taught Greek, rhetoric, and philosophy at Christ Church College in England. He was of the Empiricist movement which puts emphasis on experience, even spiritual experience, rather than on pure reason, as the rationalists maintained. Locke believed that we’re born with a blank mind, a tabula rasa, that’s filled through the five senses. The knowledge that comes from life experience is what induces reflection. 

Locke was the first to suggest if we’re all born with a blank mind it must mean we’re born equal. He believed in the natural goodness of man and that the masses could be freed from poverty through education. He participated in the “Bloodless Revolution” in England in 1688, where the decision-making in state affairs was turned over from the monarchy to a parliament.

Isaac Newton (born 1642) made his most important discoveries in a two-year period. He was professor at the University of Cambridge when he retired age twenty-two to study and write his findings on the laws of motion. He assembled his conclusions on gravitational movement, calculus, and the spectrum in his thesis Philosophiae naturalis principia mathematica or more conveniently, Principia, published in 1687. Newton sided with the philosopher Pythagoras in his conviction that everything could be explained with numbers. His conclusions on the workings of the universe - where the earth was just one of several planets that rotated around a smallish star - were mathematically infallible.

George Berkeley (born 1685) Irish philosopher and clergyman, founded the school of Idealism, where matter cannot exist independent of the mind. The mind can only be explained by a supernatural force that keeps it alive, and objects exist only because we think of them.

David Hume (born 1711) Scottish philosopher and historian, an important figure in the Empiricist school of thought, along with Locke and Berkeley, also an advocate of speculative philosophy taken from the Stoics and the Skeptics. In his essay A Treatise of Human Nature he goes opposite Descartes’ rationalist reasoning, which he considered fruitless because it did not take into consideration personal experience dictated by cause and effect and free will. Thus reality can only be conjured; why humans can only perceive themselves through sensations where we perceive good or bad according to our own needs to feel happy. cording to 

Martin Luther’s rebellion against the Church contributed to the renewed interest in science, and Galileo’s conclusions were advanced by scholars into the next century. He was a role model for his courageous stand on the separation of religious dogma and scientific research. The great thinkers of the 16th century were rationalists, a way of thinking that places emphasis on reason in obtaining knowledge. Their observations were widely studied amongst Europe’s educated.