ACT Reading Main Idea & Inference Questions: Complete Guide

ACT calls one major Reading category Key Ideas and Details.

It currently makes up roughly 44–52% of Reading.

The skills include:

• central idea;
• important details;
• sequence;
• comparison;
• cause and effect;
• logical inference.

When two passages ask you to compare authors' viewpoints, the ACT paired passages guide walks through strategy for that format specifically.

Main idea

The main idea is not:

one interesting detail.

It is the point that best covers the passage as a whole.

The scope test

A good main-idea answer should be:

• broad enough to cover most of the passage;
• narrow enough to match what the author actually discusses.

Too broad:

Technology has changed civilization.

Too narrow:

One laboratory bought a new sensor in 2019.

Better:

New low-cost sensors have changed how small research teams collect environmental data.

Inference

An inference must be supported by the text.

ACT inference is not:

What could possibly be true?

It is:

What conclusion is most strongly supported?

Minimum-proof rule

Choose the answer that requires the fewest unsupported assumptions.

If the passage says:

The new material retained more strength after heat exposure than the older material.

Valid inference:

The new material performed better on this heat-resistance measure.

Too strong:

The new material is superior in every possible use.

Detail questions

Go back to the passage.

Do not answer from memory if the text is available.

Find:

• the exact line/idea;
• then paraphrase it.

For a complete section-by-section breakdown of the redesigned exam, see our enhanced ACT guide.

Cause and effect

Watch for:

• because;
• therefore;
• led to;
• resulted in;
• prompted;
• due to.

Do not reverse cause and effect. Explore more ACT guides for other Reading and Math skills.

Original practice

Passage:

Biologists tracked a bird population before and after a wetland was restored. Two years after restoration, the number of nesting pairs had increased, but the researchers cautioned that several unusually mild winters may also have affected the population.

1

What is the main idea?

A. Mild winters always increase bird populations.
B. Bird numbers rose after restoration, although other factors may also have contributed.
C. Wetland restoration never works.
D. The researchers studied only winter temperatures.

2

Which inference is best supported?

A. The restoration definitely caused the entire increase.
B. The increase may have had more than one cause.
C. Mild winters had no effect.
D. The bird population will continue increasing forever.

Answers

1. B
2. B

Fast method

Main idea

Summarize the passage in one plain sentence before reading choices.

Inference

Ask:

What must be true or is most strongly supported?

not:

What sounds clever?

If pacing across the section is your bigger obstacle, the ACT Reading timing guide breaks down how to budget your minutes across passages.

Official sources

• ACT Reading Test Description: https://www.act.org/content/act/en/products-and-services/the-act/test-preparation/description-of-reading-test.html
• ACT Reading Tips: https://www.act.org/content/act/en/students-and-parents/high-school-success/testing-advice-for-the-act/act-reading-test-tips.html

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