Abstract: The conclusion of inductive reasoning is uncertain because the range of conclusion is broader than the range of premise. One approach of increasing the certainness of induction is searching diversiform premise. By the methods of searching evidence, giving judgement, extending feature, and choosing host, researcher found that the mechanism of diversity can explained by the much category coverage, rule of probability。In fact, the diversity effect is the consequence of implication of and the law of large numbers, which include distinguishing the difference of premise objects, detecting category information and abstracting numerical difference between diverse premise and non-diverse premise, using large number in increasing strength of conclusion

Key words: Inductive reasoning, diversity, coverage, probability, law of large numbers