In everyday speech an "argument" is a quarrel. In logic it's something calmer and more useful: a set of reasons (premises) offered to support a claim (conclusion). That's it. "You should bring an umbrella (conclusion), because it's going to rain and you hate getting wet (premises)." Once you see the premises-to-conclusion skeleton, you can check whether it actually holds up.
The premises are the support; the conclusion is what they're meant to hold up. A good argument is one where the support genuinely bears the weight.
The two questions that test any argument
To judge an argument, ask two separate things — and keep them separate, because this is where most confusion lives:
1. Is it valid? (Does the logic work?) If the premises were true, would the conclusion have to follow? This is about structure, not truth. "All cats can fly; Felix is a cat; so Felix can fly" is perfectly valid — the logic is airtight — even though a premise is false.
2. Is it sound? (Are the premises actually true?) An argument is sound only if it's valid and its premises are really true. The flying-cats argument is valid but not sound. Soundness is what you ultimately want.
Valid means the logic holds. Sound means the logic holds and the facts are real. Always check both.
This split is a powerful diagnostic. When you disagree with a conclusion, you can now pinpoint why: is the reasoning broken (invalid), or is a premise false (unsound)? "I accept your logic, but I reject premise 2" is one of the most useful sentences in clear thinking.
Deduction vs. induction
Two flavors of reasoning, good for different jobs. Deduction goes from general to specific with certainty (the Socrates example) — if valid and sound, the conclusion is guaranteed. Induction goes from specific observations to a general likelihood ("the sun has risen every day, so it'll rise tomorrow") — it never gives certainty, only strength. Most real-world reasoning, including science, is inductive: not "proven," but well-supported. Demanding deductive certainty from an inductive question is its own mistake.
The rot to watch for: logical fallacies
Fallacies are arguments that look persuasive but have a broken structure. They work by feeling right. Learn to name them and they lose their spell. A starter gallery:
Turning it on yourself
The real power move isn't spotting fallacies in your opponents — that's easy and smug. It's catching them in your own thinking, where they hide best. Steel-man the other side (argue their position at its strongest before you disagree), ask what would change your mind, and separate "I don't like this conclusion" from "this argument is actually flawed." Good reasoning is a discipline you practice on yourself first.
An argument is premises supporting a conclusion. Test it with two separate questions: is it valid (does the logic hold?) and is it sound (are the premises true?). Know that deduction gives certainty and induction gives likelihood, and learn to name the common fallacies — arguments that feel right but are structurally broken. Then apply all of it to your own thinking first.
Try this: take a strong claim you saw recently — an ad, a headline, a hot take. Find its premises and conclusion, then ask "valid? sound?" and check it against the fallacy list. With practice this becomes automatic — and the world gets a lot clearer.
Scope. An introduction to informal logic and critical reasoning; the field is deep, and some "fallacies" are context-dependent (an appeal to a genuine expert, for instance, can be reasonable). Use these as flags for closer inspection, not automatic disqualifiers.
- 📘 Thinking, Fast and Slow — Daniel Kahneman (why our reasoning goes wrong; see also The Biases That Fool Everyone)
- 📘 Being Logical — D.Q. McInerny (a short, clear primer on argument)
- 🌐 Your Logical Fallacy Is — a friendly illustrated fallacy reference
- 🌐 Stanford Encyclopedia of Philosophy — Fallacies (rigorous)