>>513095117
https://archive.org/details/logicorrightuseo00watt
table of contents in my next post

https://archive.4plebs.org/pol/thread/512205412/#512207103

Study Latin:
https://archive.org/details/familia-romana

The grammar they studied/study in the Trivium is Latin and Greek grammar.
https://en.wikipedia.org/wiki/Trivial_school

Studying Latin grammar expands your mind and together with logic and rhetoric gives you the tools of thought. Grammar in the past was taught as interconnected with logic and rhetoric, these were taught as a unified system. Furthermore grammar used to be more philosophical than now. We aren't taught any grammar at all. Read the book in the first link, study Latin with the third link, and study Euclid's Elements which teaches you logic.