Sources of knowledge: empiricism and rationalism

What this dot point is asking

This dot point belongs to Unit 1 of the TASC Philosophy course, where epistemology is introduced as the study of the nature and sources of knowledge. Having met the definition of knowledge as justified true belief, you now examine the deeper question of where justification ultimately comes from: the world delivered through the senses, or the mind reasoning on its own.

The empiricist tradition

Empiricism holds that experience derived from the senses is the source of all knowledge. John Locke argued that the mind at birth is a tabula rasa, a blank tablet, with no innate ideas printed on it. Everything we can think about arrives either through sensation, our outer experience of the world, or reflection, our inner experience of our own mental operations. Complex ideas are built from simple ideas that ultimately came from experience. David Hume sharpened this into a tool of criticism: every genuine idea must be traceable to a prior impression, a vivid sensory experience. If a supposed idea cannot be traced to any impression, Hume treats it as empty.

The rationalist tradition

Rationalism holds that reason rather than experience is the foundation of certainty in knowledge. Rene Descartes sought a truth so secure that no doubt could touch it, and found it not in the senses, which can deceive, but in pure thought: the cogito, his certainty that he exists as a thinking thing. Descartes held that some ideas are innate, placed in the mind independently of experience, including the idea of God and the basic truths of mathematics. Plato earlier argued in the Meno that an untaught slave boy can be led to geometrical truths by questioning alone, which Plato explained as recollection of knowledge the soul already possessed. For rationalists the senses give at best unreliable opinion, while reason grasps necessary, universal truths.

The case each side makes

The empiricist points to the obvious dependence of thought on experience. A person born without sight has no genuine idea of colour, which suggests concepts really do come from the senses. Hume used his impression test to challenge metaphysical notions like necessary causal connection, arguing we never actually observe a power making one event produce another, only constant conjunction. The rationalist replies that experience alone cannot deliver the necessity and universality found in mathematics: no number of observed triangles proves that all triangles must have angles summing to two right angles. Such truths seem known by reason. Rationalists also argue that learning requires some prior structure in the mind, since a truly blank slate could not organise sensory chaos into experience at all.

Toward a synthesis

The sharp opposition softened over time. Immanuel Kant argued that both sides were partly right: knowledge requires sensory input, but the mind actively structures that input using categories it supplies itself, so that, in his famous slogan, thoughts without content are empty while intuitions without concepts are blind. This suggests knowledge is a joint product of experience and reason rather than the work of either alone. For the TASC course you should be able to present the strongest version of each school, deploy a signature argument such as Hume's impression test or Plato's slave boy, and reach a reasoned judgement about how much of knowledge each can explain.