An atomic idea is a term that was popularised by Sonke Ahrens, the author of How To Take Smart Notes. He promotes use of the zettlekasten note taking methodology which, as he states, contains notes which are distilled from its source into an atomic idea. Meaning that one note will contain notes pertaining to one idea such as Computers can extend cognition. Another key feature of atomic idea notes is that they contain all the required context to understand the idea without the aid of any supplementary notes. This means that stumbling across the note at a later stage should allow you to completely understand where that note fits into what you already know. This creates a mental model for which you take notes with the thinking in mind that you’ll be teaching it to someone who doesn’t understand (your future forgetful self).