On Happiness - Epicurus
A fairly short read split into 3 parts. The first covers Epicurus' philosphy of Hedonism, which has a different meaning and practical application than the current colloquial meaning. Despite the claim in the book that Epicurus was in opposition or disagreement with the Stoics there seems to be a fair bit of overlap between the two. The philosophy itself does advocate for pursue pleasure, but in moderation, and avoiding the suffering that can occur from overindulgence. Which is the bit that seems to be commonly ignored in modern usage of the word.
The second part is about Epicurus' ideas regarding Atomic Theory, which is rather interesting in a historical science sort of way. Important to read it given the proper context for the time it was written. The way some of the ideas presented have carried forward and the emphasis on observation and not being superstituous are as valid today as when the text was penned.
The final section is some letters that rehash the first two sections and add some more points.