Here is the list that corresponds to the "Famous Rationalists" of last week.
Aristotle (384-322BC): Plato thought that ideas exist on their own, in heaven. Our souls know them before they enter our bodies, and thus truth is something our minds know innately. However, for Aristotle, we only come to knowledge by experiencing things with our senses. Universal truth is something we abstract from our experiences, not something built into our minds even before birth. Before experience, our minds are like a blank tablet with only the potential to have things written on them.
John Locke (1632-1704): We might call Locke the “founder of modern empiricism” for the way he steered philosophy, at least in Britain, away from the rationalism of continental Europe (Descartes, Spinoza, Leibniz) and toward empiricism. Like Aristotle, Locke considered our minds to be a “blank slate” (tabula rasa) prior to experiences from our senses. We have sensations of the world and reflections on the workings of our own minds that result in simple ideas (each part of a flower, the color blue). Our minds then rightly connect simple ideas into more complex ideas (a blue flower).
At the same time, Locke continued to believe that the things we experience have “substance” behind them. The substance behind our sensations is matter, and the substance behind our reflections is mind. Thus like Descartes he believed that the world consisted of two basic substances, mind and matter, in a mind-body dualism.
George Berkeley (1685-1753): With Locke, Berkeley affirmed that experience was the source of all our knowledge and denied that we have any innate knowledge. However, he disagreed with the dualism of Locke and Descartes, that mind and matter are two different substances. Locke had distinguished between two different kinds of things we experience in the material world. Primary qualities are aspects of the world that exist independently of our experiencing them (like shape) while secondary qualities are things that only exist as a result of our experiencing them (like color).
Berkeley denied this distinction—all the qualities of the world exist because someone is experiencing them, in particular, because God is perceiving them. Berkeley thus denied that any material substance underlies the world of our perception at all. Rather, “to be is to be perceived” (esse est percipi). He was an idealist, who believed that, apart from God, the only kinds of things that actually exist are ideas.
David Hume (1711-76): Hume developed and refined Locke’s empiricism to its ultimate, logical conclusion. He called Locke’s sensations “impressions,” and believed that these correspond to ideas we have in our minds. Hume also followed Locke in seeing complex ideas as conglomerates of simple ideas. But Hume strongly argued that no idea we have makes sense unless it corresponds and originates with sense impressions.
Accordingly, Hume questioned Locke and Descartes’ claims that matter and mind are substances that underlie our experiences. Berkeley had denied that matter underlies our experiences, but had accepted that idea underlies them. Hume denied both, finding the notion of underlying substance—which cannot be experienced—meaningless. Hume also questioned notions like cause and effect, the existence of God and the soul, the connection between events and moral significance. In his view, none of these connections or entities could be experienced, and thus they were meaningless notions.