Layer two: bold the most essential phrases

On a later return, bold the phrases within your highlights that are truly irreducible.

Why it works

The second layer performs a second curation pass on material that has already been curated once, further compressing the note to its absolute core. Bolding within highlights creates a visual hierarchy that lets you read only the bolded phrases in a future time-pressured context and still recover the note’s essence. This two-pass compression is also a form of spaced retrieval: the second engagement with the material reinforces earlier encoding.

How to do it

1. Return to the note for a different use — only then apply layer two.
2. Read only the highlighted sentences and bold the phrases (not whole sentences) that are the most essential.
3. Ask: "If I could keep only four words from this note, which would carry the most meaning?"
4. Bold sparingly — three to five phrases per note is usually right.

Evidence

Spaced retrieval practice (returning to material after a delay) is one of the most robustly supported learning techniques in educational psychology. Layer-two bolding occasions a second retrieval event while also producing a compressed artifact for future use. (rct)

The spaced-retrieval benefit applies to the act of returning and re-engaging, not to the specific bolding format — any active second pass would produce a similar effect.

Sources

• Dunlosky et al. (2013), distributed practice and retrieval practice among the most effective study techniques, Psychological Science in the Public Interest

Common mistake

Applying layer-two bolding in the same session as layer-one highlighting, which eliminates the spacing that is the practice’s most valuable learning mechanism.