I take notes to support reference, recollection, and accumulation. This approach was heavily influenced by Andy Matuschak’s concept of Evergreen Notes.
The best reference for learning something is usually not the most useful for applying it. I learned about random walks from the Feynman Lectures, but when I need to calculate diffusion coefficients I reference a note that just gives the answer and a few supporting details.
Reference notes should be optimized for frequently, repeated use. They should be short, focused, and linked. A note on diffusion should not explain random walks, it should link to another note which does.
Reference notes need to be totally reliable. If I have to double check the contents of a reference note it’s a bad note.
I often want to remember what I heard in a talk or at a meeting. During talks and after meetings I record ideas that came up, things I need to do, and any references I was interested in.
Unlike reference notes, recollection notes do not need to be perfect. I do not expect to reference them over and over again,
Work should accumulate over time. I write notes to capture my thinking on projects over time. These notes can hold anything from definite facts to wild speculation: the purpose is to accumulate insights.
Accumulation notes are revisable and live in version control. They are similar in many ways to Andy Matuschak’s Evergreen Notes.
I also write accumulation notes to capture brainstorming. I spend ten minutes per workday thinking of new ideas and writing down (almost) everything that comes to mind. Ideas go in Markdown files, one per day. I then prioritize these once a week, and use that prioritization to steer how I spend my time.