David Hume was a Scottish 18th century philosopher who promoted the notion of skepticism of thought, i.e. being wary of blindly following a theory or teaching. He was particularly critical of religious theories / beliefs and seemed to firmly believe in the principles of inductive thought which tends to lean towards the past acting as a reliable guide to the future. He died in 1776.
In Gemma's second YouTube blog (Living In London) she tells Bree that their mothers met at a philosophy class at which David Hume was discussed.