The Propaedia, or "Outline of Knowledge," is one of three parts of the Encyclopaedia Britannica (15th edition). Created under the direction of Mortimer J. Adler, it provides a systematic classification of all human knowledge organized into 10 Parts, 41 Divisions, and 177 Sections.
Unlike a traditional encyclopedia arranged alphabetically, the Propaedia presents knowledge hierarchically - showing how subjects relate to one another within the broader landscape of human understanding.
This site turns the Propaedia into an interactive reading guide. The original knowledge hierarchy is preserved, but every Section can now open four different reading collections:
Each Section page also includes the original hierarchical subject outline with cross-references linking related Sections across the ten Parts.
The homepage now has three different ways into the outline, each built for a different style of study:
In the Selected Fields mode, when one Part is placed at the centre and another is rotated to the top, the panel below the circle shows how they connect through cross-referenced Sections and through bridge readings that were independently recommended in both Parts.
A reading preference setting in the sidebar stores your default reading type (Oxford VSI, Wikipedia, BBC In Our Time, or Macropaedia) across the outline pages.
Section, Division, and Part pages each have their own reading-type selector inside the recommendation panel, and the homepage has separate selectors in Whole Outline and Selected Fields. Changing any of these selectors updates the shared default, so the same reading type is shown first elsewhere whenever it is available.
A reading checklist lets you mark books, articles, and episodes as done. Progress is saved locally in your browser and reflected across the site - checked items are excluded from homepage paths and bridge recommendations, and checkboxes appear on individual reading pages.
The Oxford VSI, Wikipedia, and BBC In Our Time recommendations are matched to Sections using build-time scoring plus AI-assisted mappings. Macropaedia recommendations come from the original Britannica references already attached to the Propaedia. Each mapped recommendation includes a rationale explaining why it was matched. Clicking an outline item filters the list to that branch of the outline and re-ranks the matched items inside the current selection.
Each book, article, or episode receives a score based on how closely it relates to the Section you are viewing. The scoring gives the strongest weight to direct title matches, then adds weight for subject terms, keywords, mapped outline paths, and overlap with the language used in the Section title and outline.
When you click an outline item to filter the list, the scoring also considers the sub-topics beneath that item. A resource that touches several child topics ranks above one that only matches a narrow fragment of the current branch.
The relevance percentage shown on each card is relative - the best-scoring resource in the current view is always shown as 100%, and the others are scaled proportionally.
The Whole Outline tool ignores items you have already marked done and asks a coverage-first question: which unread item adds the largest number of currently uncovered Parts, Divisions, Sections, or Subsections for the selected reading type?
After each suggested step, the covered area is updated and the next step is recalculated from what remains. If two items add the same amount of new coverage, the tie is broken in favour of the one whose new coverage is spread more widely across the outline, and then the one attached to more Sections overall.
The recommendation panels on Part and Division pages are not separate AI runs. They are rollups built from the Section-level matches already attached to the outline.
On a Part page, a reading ranks higher when it appears across more Divisions in that Part, covers more Sections, and spreads that coverage evenly rather than being concentrated in one corner. On a Division page, the same idea is applied one level down: readings are ranked by how many Sections in that Division they cover, with extra weight for broader mapped-path coverage.
The relevance percentage shown on those cards is relative to the strongest item in the current Part or Division list, not a global score across the whole site.
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