To wager is to assess the risks in two or more options and settle on the one most likely to have a favourable outcome. In his teaching, the Buddha used a wide variety of approaches to help people understand the truth of the Dhamma. Sometimes he would appeal to their better nature, saying that virtue `creates love and respect and conduces to helpfulness, non-dispute, harmony and unity'(A.III,287). At other times he targeted their concern for their future, reminding them that while goodness and integrity result in winning the respect of others, immorality can lead to a poor reputation, an uneasy conscience, perhaps even trouble with the law (M.III,164). Arguments such as these are based on observable fact. But there are some aspects of the Dhamma which are not normally accessible to direct experience, kamma and rebirth, being examples of this. Thus, the Buddha sometimes used reason when speaking on these subjects and the most interesting rational argument he used was what might be called the wager argument.
Once he was addressing an audience of well-educated people who told him that they were unable to have confidence in a doctrine `not supported by reasons' (no àkàravatã). The gist of the Buddha's talk with them was this. If kamma and rebirth are true, and one is virtuous, one will be liked, trusted and respected now, and have a favourable rebirth in the next life. If kamma and rebirth are true and one is immoral, one will have tribulations now and an unfavourable rebirth in the next life. If kamma and rebirth are not true, and one is virtuous, will still be liked, trusted and respected in this life nonetheless. Given this, a wise person can see compelling reasons for believing in kamma and rebirth and acting accordingly, or at least in acting as if they were true (M.I,402).
Those who hesitate to become Buddhist because they are unsure about the reality of rebirth, can consider this same line of reasoning. Whether or not rebirth is true, one can still act with virtue and benefit from it, still practice meditation and serenity and concentration, and still revere and respect the Buddha and be enriched by it.