Assessing the case for theism › Proof, evidence, and cumulative support

A deductive proof aims to make its conclusion unavoidable if its premises are true. A nondeductive argument supports a conclusion without guaranteeing it. Finding a wet pavement may support the hypothesis of rain even though a sprinkler could explain it. That alternative prevents a proof; it does not make the observation irrelevant.

Mackie expressly allows that individually modest arguments can have a cumulative effect. His introduction uses the comparison with a legal case: several considerations may together justify a conclusion that none establishes alone. Chapter 14 returns to their combined force. It is therefore inaccurate to say that he rejects theism simply because no isolated argument delivers certainty. His question is whether the whole body of evidence favors the divine explanation over its alternatives. Introduction, pp. 4–7; chapter 14(b).

Consider an ordinary example. A colleague repeatedly misses meetings. Illness could explain every absence. So could a calendar error. Before choosing, check what each hypothesis predicts: perhaps the colleague is answering messages from bed, or perhaps every missed meeting used an outdated invitation. Merely adding an explanation that can fit any outcome gives little help in deciding between them.

The analogy has limits. A creator is not a colleague, and a universe is not a meeting schedule. It nevertheless makes the reasoning problem visible: explaining why an observation would be unsurprising if a hypothesis were true does not, by itself, establish that hypothesis. Mackie's disagreement with theists often concerns that second step.