Consider this variant of Kartik's argument:

There are three claims in this argument:

• Your team should focus on digital marketing.
• Many customers are in their twenties.
• A recent Pew survey showed that people in their twenties spend 10% more time online than last year.

The survey results about people in their twenties make it more likely that your team should focus on digital marketing, but only if many of your customers are actually in their twenties. For example, if your customers are mostly aged 60 and above, then the Pew survey about people in their twenties wouldn't make it more likely that you should focus on digital marketing. Thus, the survey results don't make the conclusion more likely on their own. Rather, the survey results and the claim about the demographics of your customers make the conclusion more likely together.

Generally, you can determine if claims 1 and 2 make claim 3 more likely together by asking yourself: "If one of claim 1 and claim 2 is false, does the other claim still make claim 3 substantially more likely?" If yes, claim 1 and claim 2 make claim 3 more likely independently. If not, claim 1 and claim 2 make claim 3 more likely together.

In diagrams, we represent claims that make another claim more likely together by letting their arrows join:

Why is this important to understand?

If two claims make claim C more likely together, and you don't believe one of the claims, you can ignore the other claim. It doesn't make claim C more likely on its own. In contrast, if two claims make claim C more likely independently, and you don't believe one claim, then the argument might still convince you if you think the remaining claim sufficiently increases the likelihood of claim C. That's why it's important to recognize if two claims make another claim more likely together.

Practice

Let's practice distinguishing whether claims make another claim more likely together or independently. To draw an arrow from two claims that make another claim more likely together, click the arrow buttons on both claims before clicking the claim they make more likely.

If two claims make another claim more likely together, why not just put them in the same box? The reason why we should keep them in separate boxes is illustrated by the following, more complicated argument.

Kartik added a fourth claim to his argument: that online reviews of the products are mostly written by users in their twenties. This claim makes it more likely that many of your customers are in their twenties. If we put claims in separate boxes, we see which claim is made more likely by the claim about online reviews:In contrast, the information which of the two claims is made more likely by the new claim is lost if we put the two claims in the same box:To fully grasp how an argument works, and thus to equip you to critically engage with it, we should put claims into different boxes, even if multiple claims together make another claim more likely.