Deduction aims at certainty: if the premises are true, the conclusion must be. Most real reasoning is inductive: the premises make the conclusion more or less likely, never certain.

Every swan I have seen is white. So all swans are white. Reasonable for centuries, until black swans were found in Australia. Induction can be strong and still turn out wrong.

Strong and weak, not valid and invalid

Inductive arguments are judged as strong or weak. What makes one strong:

• Enough cases. Three friends liking a film says little about everyone.
• Representative cases. A survey of one neighborhood can't speak for a whole country.
• No cherry-picking. Counting hits and ignoring misses inflates confidence.
• Consistency with other evidence.

Inference to the best explanation

Often we reason from evidence to the explanation that best accounts for it. Footprints, an open window and missing cake: the best explanation might be a hungry child, not a ghost. A good explanation accounts for all the evidence, is simple, and fits what we already know.

Correlation is not causation

Ice cream sales and drownings rise together. Ice cream doesn't cause drowning; hot weather drives both. Before concluding that A causes B, ask whether B causes A, whether something else causes both, or whether it's coincidence.

Why it matters for UH

Some parts of Universal Humanism are deductive (the three apple proof). Others are supported inductively: the historical record of what happens when particular identities are placed above universal humanity. Knowing which kind of support a claim has tells you how to test it.