The idea system

Most reading apps organise by source: your notes from Atomic Habits live in one place, your highlights from Thinking, Fast and Slow in another. That's useful for reviewing a single book. It's useless for the question that matters most: what have I read, across everything, on the subject of habit?

Surfc answers that question through Ideas.

What an Idea is

An Idea is a concept that cuts across sources. When you tag a note with the Idea Justice, that note joins every other note tagged Justice — regardless of which book it came from, when you captured it, or how you phrased it.

Over time, your Ideas become the index. Open Habit and you'll see a thread assembled from James Clear, Kahneman, a podcast transcript, and a margin note you made six months ago — connected not because they're in the same book, but because they're about the same thing.

The idea canon

Surfc ships with an idea canon drawn from Mortimer Adler's Syntopicon — the reference index he compiled for the Great Books of the Western World. These include concepts like:

Angel · Animal · Art · Beauty · Being · Cause · Chance · Change · Citizen · Constitution · Courage · Custom · Definition · Democracy · Desire · Dialectic · Duty · Education · Element · Emotion · Eternity · Evolution · Experience · Fate · Form · God · Good · Government · Habit · Happiness · History · Honor · Hypothesis · Idea · Immortality · Induction · Infinity · Judgment · Justice · Knowledge · Labor · Language · Law · Liberty · Life · Logic · Love · Man · Mathematics · Matter · Mechanics · Medicine · Memory · Mind · Monarchy · Nature · Necessity · Oligarchy · One and Many · Opinion · Opposition · Philosophy · Physics · Pleasure · Poetry · Principle · Progress · Prophecy · Prudence · Punishment · Quality · Quantity · Reasoning · Relation · Religion · Revolution · Rhetoric · Same and Other · Science · Sense · Sign · Sin · Soul · Space · State · Temperance · Theology · Time · Truth · Tyranny · Universal · Virtue · War · Wealth · Will · Wisdom · World

You don't need to know all of them. The AI will suggest the most relevant ones for each note you capture, and you'll naturally gravitate toward the Ideas that matter to your reading life. If you're working through Brené Brown on Courage, Angela Duckworth on Habit, or Carol Dweck on Education, those Ideas are already waiting.

Custom ideas

The idea canon covers a lot of ground, but not everything. If you're deep into a specific thread — narrative medicine, stoic practice, or a running theme across Paulo Coelho you want to track — you can create your own Ideas.

From your Profile, tap Custom ideas, then tap the + button in the bottom right. A sheet opens. Enter the idea name (required) and an optional description — the AI uses the description when suggesting tags, so a good one improves discovery accuracy.

Tap Add to index and the idea is immediately available for tagging. A confirmation appears: "[Name]" added to your index.

Custom ideas work exactly like canonical ones: they appear in AI suggestions, gather notes over time, and sort by note volume alongside the canon.

The Ideas index

The Ideas screen shows every active Idea — ones that have at least one note attached — sorted by note volume. The ideas dominating your reading life rise to the top.

Tap any Idea to see all notes tagged to it, in reverse chronological order. This is your index: the assembled record of what you've read and thought on that subject.

Ideas vs. folders

If you've used note apps organised by folder or notebook, Ideas will feel different. A note in Surfc doesn't live in one place — it can belong to several Ideas simultaneously. A note from Grit about persisting through failure might carry Habit, Courage, and Education at the same time, appearing in all three indexes.

That's intentional. Ideas aren't containers. They're threads, and your notes pull those threads across your entire reading life.

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Next: Sources & Provenance — connecting every note to the book or article it came from.