Empirical knowledge is the kind of knowledge that is gained through experience. Strictly speaking, there is no "school of empiricism," but there are general veins of empiricist thought throughout philosophy. Most famous along these lines are various English-speaking thinkers such as Thomas Hobbes, John Locke, George Berkeley, and David Hume. In a strange way, some aspects of the thought of Emmanuel Kant can be added to this list, though he is also heavily influenced by rationalist strands of thought in continental Europe. He does believe in some forms of a priori cognition—that is, knowledge that is independent of experience.

The general idea of an empiricist philosophy is that our knowledge arises from sensation and is limited thereto. It does not hold that we have innate ideas at all. Thus, even ideas like "infinity" are formed by knowing that there could be an infinite sequence of particular experiences constructed from our finite experiences. Of course, each of these thinkers has a unique viewpoint, so "empiricist" is a single category only in a very loose sense.

The most famous account of the mind as a blank slate is that which is expressed by John Locke in his Essay Concerning Human Understanding. There, he emphasizes that everything in the mind must be derived from experience. We are born without any experiences, thus meaning that we are a kind of slate or tablet waiting to be "informed" by our experiences. Locke was no great innovator in this regard. He was taking over an old theme from Medieval and late-scholastic philosophy that was ultimately found in Aristotle. Nevertheless, for many modern thinkers, Locke's theory of knowledge was very influential—even long after it was questioned by many philosophers. (Indeed, it remained influential on the official French curriculum through the early 20th century!)

Gottfried Wilhelm Leibniz wrote a work New Essays on Human Understanding as a response to the work of John Locke. It was not published until many years after the death of both men. In the essay, there is a famous line where Leibniz quotes a so-called maxim of empiricism: Nihil est in intellectu quod non fuerit in sensu—Nothing is in the intellect which was not first in the senses. He then adds a qualifier: excipe, nisi intellectus ipse—except for the intellect itself. The idea is that while all knowledge must be derived from our sense experience, still, in order for there to be intellectual knowledge, there must be an intellect to integrate our experience. Hence, Leibniz hoped to maintain the insights of the general school of thought known as rationalism, which emphasized the direct and pre-experiential role of the human mind in the shaping of our knowledge.