With 'should', expect the best

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Someone over on the ETJ list asks how to explain the problem with should in the following sentence: If you fly on a Bombardier airplane, you should die. The intent is not to express some kind of moral outrage about Bombardier, but to suggest that their airplanes are likely to drop from the sky at any moment. Yet, that's not how most native speakers of English would interpret the above.

I'm not really sure why this should be so, though I believe that it must depend to a certain extent on the ability of the addressee to comply with the utterance. Compare:

• If you fly on a Bombardier airplane, you should arrive on time for your flight. (advice)
• If you fly on a Bombardier airplane, you should arrive on time at your destination. (prediction)

Given this, "...you should *expect* to die" fixes the problem, since expectations are, as long as you're pre-warned, somewhat within your control.

Where the verb denotes something outside of your volition, there seems to be a difference between positive outcomes and negatives (at least in this particular sentence.)

• A. If you fly on a Bombardier airplane, you should survive. (prediction)
• B. If you fly on a Bombardier airplane, you should die. (?)
• A. If you fly on a Bombardier airplane, you should be satisfied with the service. (prediction/advice)
• B. If you fly on a Bombardier airplane, you should be dissatisfied with the service. (?)
• A. If you fly on a Bombardier airplane, you should arrive on time at your destination. (prediction)
• B. If you fly on a Bombardier airplane, you should arrive late at your destination. (?)
• A. If you fly on a Bombardier airplane, you should have a pleasant trip. (prediction)
• B. If you fly on a Bombardier airplane, you should have an unpleasant trip. (?)

I'm not sure how far this observation can be generalised, but there it is.