We've seen a good number of arguments that can be weakened or strengthened by introducing or blocking alternative hypotheses. Whenever you encounter a causal argument in LR, I want you to reflexively ask yourself "Are there alternative hypotheses?" Get into that habit because this will be one of the most repetitive patterns in LR.

But, there are other less frequently recurring patterns.

Sometimes, you'll see an argument that presents the facts (the phenomena) that look a lot like an experiment. Or perhaps it even states that it is an experiment. The argument will then draw a causal conclusion, typically a hypothesis that attempts to explain the experiment. When that happens, ask yourself "How far short from ideal did this experiment fall?" because I guarantee you the (pseudo) experiment was far from ideal. And it's in that space between the real and the ideal that the weakness of the argument will be found.

Another way to approach this is to ask yourself how you would design the experiment if you wanted to test the hypothesis. If you're feeling a bit shaky on the concepts, now's a good time to review some lessons on the ideal experiment.

This type of argument is related to the arguments we've been analyzing because recall the point of running an ideal experiment is to eliminate all other alternative causes. So you can think of this pattern of arguments as the generalized form of the previous sets that we've covered.

When a Weaken or Strengthen question features a causal argument that draws its conclusion from what looks like an experiment, think back to the ideal experiment. Ask yourself: how well do the experimental conditions in the argument compare to those of the ideal experiment?

• Does the experiment involve a large sample size? Is it a random sample?
• Is there a control group? Is it also large and randomized?
• Are the subjects “blinded” to prevent the placebo effect?
• Are the researchers or observers “blinded” to prevent bias in how they collect their data or observations?
• How well are alternative hypotheses ruled out?

One way to weaken a causal argument is by showing that its experimental conditions are far from ideal.

By the same token, one way to strengthen a causal argument is by showing that its experimental conditions fall closer to the ideal.