What a Good Summary Actually Does
A common misconception is that summarizing means writing a shorter, vaguer version of a document — the same content, compressed and blurred. A genuinely useful summary does the opposite: it identifies the small number of sentences that carry the most actual information and presents those with full precision, discarding the connective tissue, examples, and repetition around them. The goal isn't to say less about everything — it's to say the same amount about the handful of things that matter most.
How Extractive Summarization Decides What Matters
There are two broad approaches to automatic summarization. Abstractive summarization generates new sentences that paraphrase the source — this is what large language models do, and it requires genuinely understanding the content well enough to rephrase it. Extractive summarization takes a different, more mechanical approach: it scores every sentence in the document and selects the highest-scoring ones verbatim, unmodified.
Extractive summarization typically scores sentences using a few reliable signals:
- Keyword density — sentences containing the words and phrases that repeat most often throughout the document are more likely to carry central ideas than sentences that only appear once
- Position — opening sentences, and often headers, tend to introduce what a section is actually about, so they get weighted slightly higher
- Sentence length — extremely short fragments rarely carry standalone meaning, so a minimum length threshold filters out noise
The advantage of this approach is that every sentence in the output is guaranteed to be accurate — it's a direct quote from the source, not a rephrasing that could subtly shift meaning. The tradeoff is that the summary reads as a series of extracted points rather than flowing prose, which is a reasonable tradeoff when the priority is speed and accuracy over readability.
Why Section-Aware Summarization Matters for Long Documents
A single executive summary works well for a short document, but a 20-page report covering five distinct topics loses important information if it's summarized as one undifferentiated block — a strong point buried in a minor section might get outscored by three mediocre points in a major section. Breaking a document into its actual sections first, using its own headers, and summarizing each section independently preserves information that a whole-document summary would flatten out.
What Automatic Summarization Doesn't Replace
An extractive summary is a fast way to decide whether a document deserves your full attention, and a useful reference for the specific facts and figures it contains. It is not a substitute for reading the full document when the decision on the other side actually matters — contracts, compliance reports, anything with legal or financial weight. Treat the summary as a triage tool: it tells you what's in the document and where to look closer, not a replacement for looking closer when it counts.