Once you know your claim, you need a way to get there from your evidence. The Logic Ladder separates deductive and inductive arguments. Writers use a handful of common patterns built on those two.
| Pattern | How it reasons | Example | Test it by asking |
|---|---|---|---|
| Examples (induction) | from several cases to a general claim | Three schools that added a later start saw attendance rise, so later starts tend to help attendance. | Are there enough cases? Are they typical? |
| Principle (deduction) | from a general rule to this case | Every club must have a faculty sponsor; the chess club has none, so it can’t be approved yet. | Is the rule true? Does this case fall under it? |
| Cause and effect | from a cause to its result, or back | The broken streetlight leaves the corner dark, so drivers can’t see walkers there. | Is there another cause? Does the cause come first? |
| Comparison | from a similar case of the same kind | The next town’s evening swim lessons filled up, so ours would too. | Are the two cases alike in the ways that matter? |
| Analogy | from a different kind of thing that shares a feature | A school without a library is like a kitchen without a pantry. | Does the shared feature matter for the claim? |
Key idea
Every argument moves from evidence to claim by some pattern: examples, a principle, cause and effect, comparison or analogy. Name the pattern, then apply its test.
Why it works
Each pattern can fail in its own way. Examples can be too few (a hasty generalization), a cause can be mistaken (false cause), an analogy can rest on a likeness that doesn’t matter (weak analogy). Knowing the pattern tells you which question will expose a weak step, in your argument or anyone else’s.
Worked example: An analogy in the Federalist
Madison, Federalist No. 10: “Liberty is to faction what air is to fire, an aliment without which it instantly expires.” What pattern is this, and does it hold up?
- It compares two different kinds of things: liberty and air, faction and fire. That is an analogy.
- The shared feature: each feeds the other. Without air, fire dies; without liberty, factions (groups pursuing their own interests) can’t form.
- The point Madison draws: removing liberty would end faction, but that cure is worse than the disease, just as removing air to stop fire would kill everything that breathes.
- The analogy holds where the feature matters: both cures destroy something essential.
Answer: An analogy, used to show why removing liberty is the wrong cure for faction.
Worked example: Name the pattern
“Since we added a bike rack by the front door, twice as many students ride to school.” What pattern is this, and what should a skeptic ask?
- It claims the rack caused more riding: cause and effect.
- Test: did anything else change? Maybe a new bike lane opened, or the weather was better this year.
- A stronger version would compare with a school that didn’t add a rack.
Answer: Cause and effect. Ask what else changed at the same time.
Common mistake
Not being able to say how an argument gets from its evidence to its claim. If you can’t name the step, you can’t judge it, and neither can your reader. Check: after each piece of evidence, finish the sentence “This supports my claim because …” and name the pattern you are using.