Permanent notes (also known as Evergreen notes) capture a single "atomic" idea. They also include links to related ideas. In the Zettelkasten system, they're created from Literature Notes, or Fleeting Notes if reference isn't required.
They should be precise, brief, and clear but use full sentences. They should include enough context for future-you to trigger a memory. It should also contain links to relevant reference notes (though I prefer to include the sources).
Each note has one or two keywords. Over time, visible "clustering" of your thinking begins to emerge and new questions naturally arise. Tools like Roam, Obsidian, and Bear have built-in tools for visualising these clusters.
Cover image from Close up of a zero watt light bulb from Wikimedia.
Sönke Ahrens. How to Take Smart Notes: One Simple Technique to Boost Writing, Learning and Thinking: For Students, Academics and Nonfiction Book Writers. CreateSpace, North Charleston, SC, 2017. ISBN 978-1-5428-6650-7. ↩