Tools for thought should be flexible in their use

Paper is still the best tool for thought. With paper you can write, draw, cut, fold, and organize your ideas however you like. There is little difference between writing text on the page and doodling in the sidelines. On a computer however, these may well require separate apps; typically Applications are designed for authoring not thinking.

Ideally a computer-based tool for thought would work primarily with manipulating data and give the user agency to use their own representations and workflow around that data. It would not create distinction between drawings, text, videos, or audio, and the same functions, manipulations, and keyboard shortcuts should work the same in each of these mediums. Commenting on text should be no different than commenting on video, and uses the same function across all mediums.

If everything is represented through data, it should be possible to transform from one medium to another. For example, I could change the representation of a spaced repetition deck to be turned into a video.