Logic distinguishes two fundamentally different kinds of argument based on the relationship between their premises and their conclusion. A valid deductive argument is structured so that if its premises are true, its conclusion is guaranteed to be true as well, with no possible way for the premises to hold while the conclusion fails. An inductive argument works differently: its premises can provide genuine support for its conclusion, sometimes very strong support, without ever fully guaranteeing it — an inductive conclusion follows only with some degree of probability, however strong the supporting evidence becomes.
Deduction moves from general premises to a conclusion that can't fail
A classic deductive argument, like "all mammals are warm-blooded; a dog is a mammal; therefore, a dog is warm-blooded," has a very specific logical property: if both premises are actually true, the conclusion is guaranteed to be true as well, with absolutely no logically possible way for the premises to hold while the conclusion somehow fails. This guarantee is a structural feature of the argument's own logical form, not something that depends on gathering more supporting evidence — a genuinely valid deductive argument's conclusion is already as certain as its premises are, the moment the argument's structure is confirmed to be logically valid, with no further evidence needed or even relevant to strengthen that underlying logical guarantee.
Induction moves from specific observations to a conclusion that stays uncertain
An inductive argument, like "every swan observed so far has been white; therefore, all swans are white," works quite differently: even if every individual premise, every specific past observation cited, is completely true, the conclusion still doesn't follow with logical certainty, since it's entirely possible, without any logical contradiction at all, for all the past observations to be true while a future or previously unobserved swan turns out not to be white. Gathering considerably more supporting observations can make an inductive conclusion more probable, and inductive reasoning is completely indispensable to how science and everyday reasoning actually work in practice, but no finite quantity of supporting observations, however large, ever converts an inductive argument's conclusion into a fully guaranteed one the way a genuinely valid deductive argument's structure already does.
What we're still unsure about
The formal distinction between deductive certainty and inductive probability is precisely defined, settled logic, not a matter of genuine dispute. What remains a genuinely live and actively debated question in the philosophy of science is exactly how to justify relying on inductive reasoning at all, given that induction's own reliability can't itself be established through a strictly deductive argument, and attempting to justify induction by appealing to its own past track record of working reasonably well is itself a form of inductive reasoning, arguably begging the very question being asked — this classic problem of induction, first clearly posed by the philosopher David Hume, remains a genuinely unresolved and actively discussed issue in philosophy, despite induction's obvious, continued indispensability to how science and everyday reasoning both actually work.
This sits inside Inductive vs. Deductive Reasoning, one of seven topics in Logic, one of five domains in Philosophy, one of seventeen subjects the app can quiz you on.