John Locke

Locke is the founder of British empiricism — the view that all knowledge comes from experience — and one of the architects of modern liberal politics. He argued that the mind at birth is a tabula rasa, a blank slate, and that every idea we have is built up out of sensations and reflections on sensations. There are no innate ideas, no Platonic Forms accessible to pure reason.

In politics he argued, against the divine right of kings, that legitimate government rests on the consent of the governed and exists to protect natural rights: life, liberty, and property. If a government violates these, the people may rightfully overthrow it. Jefferson copy-pasted this into the Declaration of Independence with the words slightly rearranged.

Locke was also a physician, a colonial administrator, and (notoriously) an investor in the slave trade — his political theory of universal rights coexisted with this in ways his readers still wrestle with.