Summary

The sample used in an inductive inference is relevantly different from the population as a whole.

Examples

1. To see how Canadians will vote in the next election we polled a hundred people in Calgary. This shows conclusively that the Reform Party will sweep the polls. (People in Calgary tend to be more conservative, and hence more likely to vote Reform, than people in the rest of the country.)
2. The apples on the top of the box look good. The entire box of apples must be good. (Of course, the rotten apples are hidden beneath the surface.)

Proof

Show how the sample is relevantly different from the population as a whole, then show that because the sample is different, the conclusion is probably different.