How do deductive and inductive arguments fundamentally differ?

Question

Accepted Answer

Deduction is binary (valid or not) and necessitating; induction is probabilistic (more or less likely) and defeasible.
The clean contrast across the two argument types:

Dimension
Deductive
Inductive

Verdict type
Binary: valid / invalid
Probabilistic: more / less likely

Premises→conclusion
If premises true, conclusion must be true
If premises true, conclusion is probably true

Following
Conclusion follows necessarily
Conclusion follows probably

Denying conclusion
Logically inconsistent to assert premises and deny conclusion
Logically consistent to assert premises and deny conclusion (just improbable)

The deepest line: in a valid deductive argument, accepting the premises and rejecting the conclusion is a contradiction; in a strong inductive argument it's merely unlikely, not contradictory. That's why induction can always be overturned by new data and deduction cannot.
Tip: Deduction preserves certainty (truth in → truth out, guaranteed); induction creates new content by generalising — which is exactly why it can be wrong even with true premises.

Dimension	Deductive	Inductive
Verdict type	Binary: valid / invalid	Probabilistic: more / less likely
Premises→conclusion	If premises true, conclusion must be true	If premises true, conclusion is probably true
Following	Conclusion follows necessarily	Conclusion follows probably
Denying conclusion	Logically inconsistent to assert premises and deny conclusion	Logically consistent to assert premises and deny conclusion (just improbable)