Main idea, title and purpose

English (Précis and Composition) · Comprehension. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

The main idea is the one point that the whole passage is written to make. Every sentence supports it, explains it or gives an example of it. A detail is true but covers only part of the passage.

Test each option with one question: does it cover all of the passage, and nothing more? Wrong options are usually too narrow (one detail), too broad (the general subject, which the passage only partly treats), or not stated at all. The best title is the main idea in a few words.

The writer's purpose is what the passage is meant to do: to inform, explain, describe, narrate, persuade or criticise. Verbs such as should and must, and strong judging words, signal persuasion.

Rules to remember

Main idea = topic + what the writer says about it. A topic alone (water, libraries) is not a main idea.
Look hardest at the first and last sentences; the point usually stands there.
After but, yet and however comes the writer's real view; what stands before is often the view being answered.
Too narrow = one detail or example. Too broad = a subject far wider than the passage.
A good title is short, covers the whole passage and matches its tone.
Purpose words: inform (facts), explain (how or why), describe (a scene), narrate (events), persuade (should, must), criticise (faults).
An example or story in a passage serves the point; it is never the point itself.

Common mistake

Candidates choose an option because it repeats words from the passage, although it covers only one detail. Ask whether the option would still fit if that one sentence were removed.

Worked example

Street trees are often seen as decoration. Yet a row of mature trees lowers the temperature of a road by several degrees, slows rainwater before it floods the drains, and filters dust from the air. A city that fells them for wider roads pays later in heat and floods. Best title? A How Trees Grow, B The Problem of Urban Floods, C Trees as Working Parts of a City, D Wider Roads for Modern Cities.

The turn comes at Yet: trees are not just decoration, they do useful work.
The three services (cooling, slowing rain, cleaning air) all support that point.
B covers only one detail. A is not discussed. D states what the writer warns against.
C covers the whole passage: trees do practical jobs for a city.

Answer: C, Trees as Working Parts of a City.

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