# Categorization > [!quote] As far back as the fourth century BCE, Aristotle attempted to > classify all knowledge into ten broad themes. In the sixteenth century, > English philosopher Francis Bacon argued that all human knowledge could be > sorted into just three categories: memory, reason, and imagination. In the > twentieth century, the Indian librarian Shiyali Ramamrita Ranganathan proposed > classifying knowledge by personality, matter, energy, space, and time. > > <p align=right><i>Building a Second Brain</i>, Ch. 11, Tiago Forte</p> - [[tagging|Tags]] - [[folder|Folders]] - When categorizations are used, colors can be used to enhance the visualization. See [[color-scheme]] for details. ## Folder Use folder for different ==nature== of notes. For example: ``` vault ``` These categorizations are ==mutually exclusive==. ## Coloring - Refer to [[color-scheme]] for detailed discussion. - [visionOS system colors](https://developer.apple.com/design/human-interface-guidelines/color#visionOS-system-colors) shall be used throughout platforms. - Other [[apple|Apple]] systems default color has both light and dark palette. - visionOS has only dark palette, which avoids confusion and fits the translucent theme in Obsidian. - Backup candidate: [Google 2014 Material Design Palette](https://m1.material.io/style/color.html#color-color-palette).