Thomas Reid (1710–1796) was the founder of Scottish Common Sense Philosophy, which was prominent in English thought during the first half of the nineteenth century, and was revived by G.E. Moore (1873–1958) in his attack on idealism in the twentieth century. Reid’s basic contribution was a criticism of the doctrine of ideas in philosophy, which in his own time was famously deployed by David Hume (1711–1776), although it had strong predecessors in John Locke (1632–1704) and George Berkeley (1685–1783).

Reid believed that it is impossible that what we know are sensations or ideas in the mind because this can’t account for the immediacy of our experience of objects present to the senses, motion, or our experience of our own selves. Reid thought that we directly know real objects in the world, just like we assume in common sense. For example, when you look at a computer screen as you type, you do not perceive the idea of the screen, but rather the screen itself. His common sense was to insist on the location of the knower directly in the world, with no mediation in the mind by ideas, sensations, or impressions.