A Treatise of Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects, published in 1738 and better known in its shortened version as A Treastise of Human Nature by David Hume revolutionised philosophy and overturned previous thinking on human behaviour and ethics.
The book explores human perception, understanding, imagination, morality and virtue, how these are constructed, and how they affect how we relate to the world.
It’s a book in three parts, a massive work which, when it was originally published, was not at all successful. Hume decided the book needed to be reworked to make it more readable, and published An Enquiry Concerning Human Understanding in 1748. Nobody liked that one either.
The book has subsequently influenced several great thinkers from Kant to Einstein, and while Hume’s work was not appreciated widely in it’s day, he was nevertheless considered by his peers in the Scottish Enlightment to be one of the foremost philosophers of his generation.