AI Tutor
Imagine you are a detective investigating a broken window at a museum. You find mud on the sill, a dropped flashlight, and a flyer for a pizza parlor across the street.
All three are facts, but only two help you prove how the burglar got in. Reading history works the exact same way.
The main topic is what the whole passage is about, while a key detail is a specific fact or piece of evidence that directly proves or explains that topic.
How do you test whether a fact is truly a key supporting detail or just an extra detail? Let's use a simple filter.

The 'Because' Test

To check a detail, turn the topic into a statement and add the word because right before the detail. If the sentence makes logical sense, the detail directly supports the topic.
What does this look like when reading an actual historical source? Let's look at a report on ancient Roman aqueducts.

Worked Example: Roman Aqueducts

Read this short excerpt: (1) Roman aqueducts carried fresh water from mountain springs into cities over dozens of miles. (2) Many aqueduct bridges featured beautiful stone arches. (3) Underground pipes delivered this water directly into public baths, fountains, and private homes.
Suppose your topic is: Aqueducts provided essential water supplies to Roman citizens. Let's test each sentence to find the key details.