---
title: "Weighing a Source's Reliability"
description: "Judge how much weight a source can carry: who made it, when, for whom, and what they were in a position to know. Reliability is a question about one specific claim, not a label stuck on a whole docume"
canonical: https://lightmysky.com/learn/history/weighing-a-sources-reliability-mt_24TQ9c30NI
source: https://lightmysky.com/learn/history/weighing-a-sources-reliability-mt_24TQ9c30NI.md
retrieved: 2026-09-12
---

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# Weighing a Source's Reliability

Judge how much weight a source can carry: who made it, when, for whom, and what they were in a position to know. Reliability is a question about one specific claim, not a label stuck on a whole document.

Subject: History · Area: Historical Thinking · Ages 14 to 16
Page: https://lightmysky.com/learn/history/weighing-a-sources-reliability-mt_24TQ9c30NI

## Ready when they can

- State who made a source, when, and for which audience, and say how each of those changes its weight
- Separate what a source is strong evidence for from what it is weak evidence for
- Explain why a one-sided source can still be good evidence of what its author wanted believed
- Say what would have to turn up for you to change your judgement about a source

## Lesson: How much weight can a source carry

Never ask if a document is reliable in general. Ask what this document is strong evidence for. Fix three facts first: who made it, when, and for which audience. Each of those tilts the message, so each changes the weight.

**Example.** Take two writers on empire, one defending it and one attacking it. The same facts feed opposite verdicts once you place each maker first. Judge claim by claim: a letter can be strong evidence for what soldiers believed yet weak evidence for how many of them there were.

A one sided source can still be good evidence. It may be weak on the facts it slants, yet strong on what its author wanted readers to believe. Bias leaves clues in word choice, missing voices and loaded pictures, so compare two framings of one event and list what each leaves out.

**Tip.** Show an open mind by naming what would change your call. Say plainly what would have to turn up for you to change your judgement, and change it when that evidence arrives. Sourcing sits inside your answer, not as a label on the whole document.

**Recap.** Weigh each claim by maker, moment and audience, and say what would change your mind.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Troy: Myth or History?](https://lightmysky.com/learn/history/troy-myth-or-history-mt_aXNlkbAeIk)
- [Historical Sources on Ancient Egypt](https://lightmysky.com/learn/history/historical-sources-on-ancient-egypt-mt_bhEuF-CCuY)
- [Hidden Voices of Greece and Rome](https://lightmysky.com/learn/history/hidden-voices-of-greece-and-rome-mt_c-F__Qe23X)
- [Evidence Versus Interpretation](https://lightmysky.com/learn/history/evidence-versus-interpretation-mt_Lu4H4mbsqO)

## Opens up

- [Reading a Source in the World That Made It](https://lightmysky.com/learn/history/reading-a-source-in-the-world-that-made-it-mt_S5EPefrFAi)
- [Telling a Cause From a Coincidence](https://lightmysky.com/learn/history/telling-a-cause-from-a-coincidence-mt_SN1oFNj2gb)