Empiricism says that all knowledge is derived from sensory experience. Rejecting the idea that we come into the world imbued with innate ideas, empiricists say that we formulate ideas by assessing the evidence of our experience, especially sensory experience (i.e. that which we see, hear and feel). By applying inductive reasoning (that is to say, drawing general conclusions from specific experiences), we arrive at knowledge. Empiricism is thus the basis of modern science, since it demands that all hypotheses be proven (or be capable of being disproved) by observation.
Empiricism has its roots in antiquity, when Aristotle argued for the importance of observation in order to understand the world around us (see Aristotelianism here). His notion of the tabula rasa was taken up by the Stoics, among others. In the medieval period, Avicenna developed the concept, arguing that it is from ‘empirical familiarity with objects in this world’ that ‘one abstracts universal concepts’. Francis Bacon (1561–1626) then used empirical evidence as the basis of inductive reasoning within a scientific context to birth the modern scientific method (see here).
Into the age of Enlightenment, and European philosophy was for a time divided between the rationalists dominant in continental Europe and the empiricists who thrived in Britain – most notably George Berkeley, David Hume and John Locke. Locke made a fairly moderate argument that most knowledge derives from experience but some (such as the existence of God) may be arrived at rationally. He rejected the existence of innate ideas on the basis that no single idea applies universally across all humans. Hume, however, took a harder line, arguing that all knowledge is acquired from experience, even our capacity to reason. Moreover, since we cannot be sure that what has happened in the past will happen again, drawing conclusions from past experience is without merit. Because we saw the moon last night, for instance, does not mean it will necessarily be there tonight. This led him to the conclusion that there are no natural laws, only theories we choose to believe based on custom and instinct. All that we can truly believe, then, is that which our sensory experience shows us to be.
Putting all one’s eggs in the empiricist basket
Berkeley devised an alternative, even more extreme form of empiricism (in part inspired by his fear that Hume’s conclusions threatened religious faith) that saw him argue against the very existence of matter. Things only exist, he suggested, to the extent that they are perceived (see his idea of ‘immaterialist idealism’ in Idealism here) – an idea that was further developed by phenomenalist philosophers (including John Stuart Mill) in the 19th century. Into the 20th century, logical empiricists attempted to synthesize the ideas of British empiricism with the mathematical logic of, for example, Bertrand Russell and Ludwig Wittgenstein. Today, empiricism and science are often taken as one and the same thing. Yet no lesser figure than Einstein warned against putting all one’s eggs in the empiricist basket:
I say that true knowledge is to be had only through a philosophy of deduction. For it is intuition that improves the world, not just following a trodden path of thought. Intuition makes us look at unrelated facts and then think about them until they can all be brought under one law. To look for related facts means holding onto what one has instead of searching for new facts. Intuition is the father of new knowledge, while empiricism is nothing but an accumulation of old knowledge.