Philosophy in the modern world is a self-conscious discipline. It has managed to define itself narrowly, distinguishing itself on the one hand from religion and on the other from exact science. But this narrowing of focus came about very late in its history—certainly not before the 18th century. The earliest philosophers of ancient Greece were theorists of the physical world; Pythagoras and Plato were at once philosophers and mathematicians, and in Aristotle there is no clear distinction between philosophy and natural science. The Renaissance and early modern period continued this breadth of conception characteristic of the Greeks. Galileo and Descartes were at once mathematicians, physicists, and philosophers; and physics retained the name natural philosophy at least until the death of Sir Isaac Newton (1642–1727).

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Had the thinkers of the Renaissance been painstaking in the matter of definition (which they were not), they might have defined philosophy, on the basis of its actual practice, as “the rational, methodical, and systematic consideration of humankind, civil society, and the natural world.” Philosophy’s areas of interest would thus not have been in doubt, though the issue of what constitutes “rational, methodical, and systematic consideration” would have been extremely controversial. Because knowledge advances through the discovery and advocacy of new philosophical methods and because these diverse methods depend for their validity on prevailing philosophical criteria of truth, meaning, and importance, the crucial philosophical quarrels of the 16th and 17th centuries were at bottom quarrels about method. It is this issue, rather than any disagreement over subject matter or areas of interest, that divided the greatest Renaissance philosophers.

The great new fact that confronted the Renaissance was the immediacy, the immensity, and the uniformity of the natural world. But what was of primary importance was the new perspective through which this fact was interpreted. To the Schoolmen of the Middle Ages, the universe was hierarchical, organic, and God-ordained. To the philosophers of the Renaissance, it was pluralistic, machinelike, and mathematically ordered. In the Middle Ages, scholars thought in terms of purposes, goals, and divine intentions; in the Renaissance, they thought in terms of forces, mechanical agencies, and physical causes. All of this had become clear by the end of the 15th century. Within the early pages of the Notebooks of Leonardo da Vinci (1452–1519), the great Florentine artist and polymath, occur the following three propositions:


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The Metropolitan Museum of Art, New York; The Jefferson R. Burdick Collection, gift of Jefferson R. Burdick (accession no. 63.350.202.25.19); www.metmuseum.org

Modern philosophy

The rise of empiricism and rationalism

The scientific contrast between Vesalius’s rigorous observational techniques and Galileo’s reliance on mathematics was similar to the philosophical contrast between Bacon’s experimental method and Descartes’s emphasis on a priori reasoning. Indeed, these differences can be conceived in more abstract terms as the contrast between empiricism and rationalism. This theme dominated the philosophical controversies of the 17th and 18th centuries and was hardly resolved before the advent of Immanuel Kant.

The empiricism of Francis Bacon

Sir Francis Bacon was the outstanding apostle of Renaissance empiricism. Less an original metaphysician or cosmologist than the advocate of a vast new program for the advancement of learning and the reformation of scientific method, Bacon conceived of philosophy as a new technique of reasoning that would reestablish natural science on a firm foundation. In the Advancement of Learning (1605), he charted the map of knowledge: history, which depends on the human faculty of memory, poetry, which depends on imagination, and philosophy, which depends on reason. To reason, however, Bacon assigned a completely experiential function. Fifteen years later, in his Novum Organum, he made this clear: Because, he said, “we have as yet no natural philosophy which is pure,…the true business of philosophy must be…to apply the understanding…to a fresh examination of particulars.” A technique for “the fresh examination of particulars” thus constituted his chief contribution to philosophy.


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Thomas Hobbes, detail of an oil painting by John Michael Wright; in the National Portrait Gallery, London.

Hobbes’s account of what philosophy is and ought to be clearly distinguished between content and method. As method, philosophy is simply reasoning or calculating by the use of words as to the causes or effects of phenomena. When a person reasons from causes to effects, he reasons synthetically; when he reasons from effects to causes, he reasons analytically. (Hobbes’s strong inclination toward deduction and geometric proofs favoured arguments of the former type.) His dogmatic metaphysical assumption was that physical reality consists entirely of matter in motion. The real world is a corporeal universe in constant movement, and phenomena, or events, the causes and effects of which it is the business of philosophy to lay bare, consist of either the action of physical bodies on each other or the quaint effects of physical bodies upon minds. From this assumption follows Hobbes’s classification of the fields that form the content of philosophy: (1) physics, (2) moral philosophy, and (3) civil philosophy. Physics is the science of the motions and actions of physical bodies conceived in terms of cause and effect. Moral philosophy (or, more accurately, psychology) is the detailed study of “the passions and perturbations of the mind”—that is, how minds are “moved” by desire, aversion, appetite, fear, anger, and envy. And civil philosophy deals with the concerted actions of people in a commonwealth—how, in detail, the wayward wills of human beings can be constrained by power (i.e., force) to prevent civil disorder and maintain peace.

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Hobbes’s philosophy was a bold restatement of Greek atomistic materialism, with applications to the realities of early modern politics that would have seemed strange to its ancient authors. But there are also elements in it that make it characteristically English. Hobbes’s account of language led him to adopt nominalism and to deny the reality of universals. Bacon’s general emphasis on experience also had its analogue in Hobbes’s theory that all knowledge arises from sense experiences, all of which are caused by the actions of physical bodies on the sense organs. Empiricism has been a basic and recurrent feature of British intellectual life, and its nominalist and sensationalist roots were already clearly evident in both Bacon and Hobbes.