Although it is sometimes claimed that consuming caffeine at high level

This is a causality argument: too much coffee consumption leads to insomnia. However, what if those in the study were already suffering from insomnia, and in order to cope with it (I think we've all been here ), they began to imbibe large amounts of caffeine? Therefore, in order for the argument to hold true, we have to discount the possibility that sleep deprivation turned the insomniacs into caffeine drinkers.

A. Consumption of caffeine from sources other than coffee, tea, and soft drinks is unlikely to cause insomnia.

We are focused on the link between caffeine and insomnia, not on caffeine across different beverages (which conceivably could differ dramatically).

B. Caffeine consumption is the only commonly occurring cause of insomnia.

Even if this is the case, the argument does not depend on this statement. There could be other commonly occurring causes of insomnia the argument can still hold true: those who drink caffeine are likely to suffer from insomnia.

C. People suffering from insomnia do not typically respond to their lack of sleep by consuming much more caffeine

than they would if they did not suffer from insomnia.

Here we have it: poor insomniacs, innocent in the sin of caffeine consumption , suddenly began consuming it in large quantities. If that is the case, then we cannot say that caffeine causes insomnia; rather insomnia causes caffeine consumption.

D. The only evidence available to show whether caffeine causes insomnia is statistical evidence showing correlations

between caffeine consumption and insomnia.

The argument does not depend on the statistical evidence mentioned in the argument. There could be other forms of evidence that show the link between caffeine and insomnia. If so, the existence of that new evidence would in no way undermine the argument.

E. Anyone who regularly consumes caffeine in more than moderate quantities will suffer from insomnia.

The argument simply claims a link between caffeine consumption and insomnia. It does not rely on the assumption that anyone who consumes excessive caffeine will suddenly become a red-eyed ranting insomniac.

Answer: C.


Hope that helps!