Reading is not the same as receiving. When a careful reader gets to the end of a long piece, what they carry away is not a copy of the sentences. It is a structure they built while moving through the text. Cognitive scientists have a good account of this. Walter Kintsch’s construction-integration model describes comprehension as three nested representations the reader assembles as they go.
The surface representation is the literal words and syntax: the substance a screen-reader would see. The textbase is the propositional meaning: what the sentences claim, stripped of phrasing. The situation model is the deeper picture: what the text is about in the world, how its argument hangs together, how it connects to everything the reader already knows. Understanding, in any usable sense, lives in the situation model. A reader who has only the textbase can answer questions; a reader who has built a situation model can do something with the material a week later.
the literal words and syntax on the page
the propositional meaning — what the sentences claim
the mental model of what the text is about in the world
A summary helps with the textbase. Lasting understanding lives in the situation model — the layer a reader has to build for themselves.
This matters for product design. A summarizer can hand back a clean textbase. It cannot hand back a situation model, because the situation model has to be built by the person doing the reading. The work of selecting, organizing, connecting, and integrating new material with prior knowledge is not a bonus feature of comprehension. It is the thing itself.
Anything that bypasses that work produces fluency (the feeling of having understood) without the underlying structure. The reader feels done; a week later they cannot reconstruct what they read. The clean output of a model and the durable understanding of a person are two different artifacts.