Modern philosophy is philosophy developed in the modern era and associated with modernity. It is not a specific doctrine or school (and thus should not be confused with Modernism), although certain assumptions are common to much of it, which helps to distinguish it from earlier philosophy.

The 17th and early 20th centuries roughly mark the beginning and the end of modern philosophy. How much of the Renaissance should be included is a matter of dispute, as is whether modernity ended in the 20th century and has been replaced by postmodernity. How one answers these questions will determine the scope of one's use of the term "modern philosophy."

How much of Renaissance intellectual history is part of modern philosophy is disputed: The Early Renaissance is often considered less modern and more medieval compared to the later High Renaissance. Later, by the 17th and 18th centuries, the major figures in philosophy of mind, epistemology, and metaphysics were roughly divided into two main groups. The "Rationalists," mostly in France and Germany, argued all knowledge must begin from certain "innate ideas" in the mind. Major rationalists were Descartes, Baruch Spinoza, Gottfried Leibniz, and Nicolas Malebranche. The "Empiricists," by contrast, held that knowledge must begin with sensory experience. Major figures in this line of thought are John Locke, George Berkeley, and David Hume (These are retrospective categories, for which Kant is largely responsible). Ethics and political philosophy are usually not subsumed under these categories, though all these philosophers worked in ethics, in their own distinctive styles. Other important figures in political philosophy include Thomas Hobbes and Jean-Jacques Rousseau.

In the late 18th century Immanuel Kant set forth a groundbreaking philosophical system that claimed to bring unity to rationalism and empiricism. Whether or not he was right, he did not entirely succeed in ending philosophical disputes. Kant sparked a storm of philosophical work in Germany in the early nineteenth century, beginning with German idealism. The characteristic theme of idealism was that the world and the mind equally must be understood according to the same categories; it culminated in the work of Georg Wilhelm Friedrich Hegel, who among many other things said in the Preface to his Elements of the Philosophy of Right that "The real is rational; the rational is real."

Hegel's work was carried in many directions by his followers and critics. Karl Marx appropriated both Hegel's philosophy of history and the empirical ethics dominant in Britain, transforming Hegel's ideas into a strictly materialist form, setting the grounds for the development of a science of society. Søren Kierkegaard, in contrast, dismissed all systematic philosophy as an inadequate guide to life and meaning. For Kierkegaard, life is meant to be lived, not a mystery to be solved. Arthur Schopenhauer took idealism to the conclusion that the world was nothing but the futile endless interplay of images and desires, and advocated atheism and pessimism. Schopenhauer's ideas were taken up and transformed by Nietzsche, who seized upon their various dismissals of the world to proclaim "God is dead" and to reject all systematic philosophy and all striving for a fixed truth transcending the individual. Nietzsche found this not grounds for pessimism, but the possibility of a new kind of freedom.

Nineteenth-century British philosophy came increasingly to be dominated by strands of British Idealism, which incorporated neo-Hegelian and German Idealist thought. As a reaction to this, philosophers such as Bertrand Russell and George Edward Moore began moving in the direction of analytic philosophy, which was essentially an updating of traditional empiricism to accommodate the new developments in logic of the German mathematician Gottlob Frege.

Renaissance humanism emphasized the value of human beings (see Oration on the Dignity of Man) and opposed dogma and scholasticism. This new interest in human activities led to the development of political science with The Prince of Niccolò Machiavelli. Humanists differed from Medieval scholars also because they saw the natural world as mathematically ordered and pluralistic, instead of thinking of it in terms of purposes and goals. Renaissance philosophy is perhaps best explained by two propositions made by Leonardo da Vinci in his notebooks:

In a similar way, Galileo Galilei based his scientific method on experiments but also developed mathematical methods for application to problems in physics. These two ways to conceive human knowledge formed the background for the principle of Empiricism and Rationalism respectively.