Acknowledging and Working With Source Discrepancies

Instructor: Elizabeth Foster

Elizabeth has been involved with tutoring since high school and has a B.A. in Classics.

Have you ever read one thing in one book, and a totally contradictory thing in another book? That's called a source discrepancy. In this lesson, you'll learn how to deal with that when you're writing a paper.

Source Discrepancies

Have you ever tried to read some books for a paper, only to find that all your books disagree with each other? That's called a source discrepancy, a disagreement between two sources about the same thing.

Primacy sources (sources written by people who were there at the time) can disagree if the two authors had different perspectives on the event, if one of them was lying, or for all kinds of other reasons.

Secondary sources (sources written after the fact) can disagree if they were based on different primary sources or if they interpreted the primary sources differently. Say we have two primary sources, Source A and Source B. If Source A and Source B disagree, then historians who use only Source A will disagree with historians who use only Source B. And historians who use both can also disagree if they have different opinions about the two sources.

In this lesson, we'll go over how to deal with source discrepancies in your own academic work.

An Example: The Battle of Cannae

As an example of a source discrepancy, we'll use two different reports of the Battle of Cannae. The Battle of Cannae took place in Italy in 216 BC. In this battle, the Roman army faced off against the Carthaginians. The battle was a crushing defeat for the Romans, and many Roman soldiers died.

Our two big ancient sources for this battle are two historians, Polybius and Livy. Both of them are secondary sources, meaning that they weren't there at the time. They disagree on exactly how many soldiers died at Cannae.

  • Polybius says that 70,000 Roman soldiers and about 5,700 Carthaginians died.
  • Livy says that about 50,000 Romans and 8,000 Carthaginians died.

To analyze the discrepancy in these sources, we'll ask 3 important questions.

Questions to Ask

Question 1: 'What's the source of each author's information?'

Polybius was born around 200 BC, 16 years after the battle. He didn't fight in it, but he could have talked to people who did, so he probably used primary sources. Livy lived decades later and probably used Polybius as a source but did the math a little differently. It's also very likely that Livy used information from another historian, Quintus Fabius Pictor, but that history has been lost and we don't know where Quintus Fabius Pictor got his numbers from at all.

Livy, presumably in the throes of considering his sources.

Question 2: 'Is there a plausible motive for either author to lie or present things in a certain way?' For primary sources, could the person be lying to make himself look good or cover up for someone else? For secondary sources, does the historian have a bias that might lead him to twist the facts?

In our case, there's an obvious reason to pick on Livy. Most scholars agree that Livy was really invested in making Rome look good. So you can see how he could have been motivated to bump down the casualty numbers a little, to make it look like Rome didn't get quite so badly flattened.

Question 3: 'Bearing the first two answers in mind, which (if any!) source is more credible?'

This is the step where you pull together all your reasoning to decide which source to base your argument on. You can also bring in other evidence here - other sources, the opinions of different scholars in the field, archaeological evidence, etc.

On the one hand, based on other things we know about Roman armies, Polybius' numbers seem almost too big. But if the Romans brought in extra cavalry reserves for the big battle, it could have worked. When you combine that with Polybius being historically closer to the events and Livy having an obvious bias, most historians take Polybius as more credible. But you can see how it would be possible to argue both sides, especially since one of Livy's sources has been lost.

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