Philosophy & Critical Thinking: Assumption surfacing

What you'll be able to do: Find the premise your argument depends on that you never stated because it felt like common sense, the kind that, once named, turns out to be exactly what's in dispute.

The premise that feels like a fact

A student argues that the human good consists in rational activity done well. The reasoning sounds tight. Surfaced, it depends on a premise nobody stated: that humans have a single characteristic function at all, the way a knife has the function of cutting.

That's Aristotle's own move (Nicomachean Ethics I.7), reconstructed:

P1. Anything with a characteristic function has its good in performing that function well.
P2. Humans have a characteristic function, something distinctive to humans, not shared with plants (nutrition, growth) or animals (perception).
P3. That distinctive function is activity of the rational part of the soul.
C. Therefore the human good (eudaimonia) is activity of the soul in accordance with reason, done well, over a complete life.

P2 is the unstated assumption doing the real work: that things have purposes the way artefacts do, and that a species can have a "characteristic function" in the same sense a tool has one. Aristotle moves past it quickly. Modern virtue ethicists split exactly here. Philippa Foot defends a version of the function argument, others reject the leap from "characteristic activity" to "good" outright. Surfacing the premise doesn't refute the argument. It shows a defender precisely where the remaining work is.

Worked example: the cogito's larger argument

The cogito itself , "I think, therefore I am", is close to bulletproof. The substance dualism Descartes builds on top of it in Meditation VI is not, and the gap is a textbook case of a hidden assumption:

P1. I can clearly and distinctly conceive of my mind existing without my body.
P2. Whatever I can clearly and distinctly conceive as separable, God can create as separate, so it is really possible for them to exist apart.
C. Therefore my mind is really distinct from my body.

The unstated premise is P2's underlying claim: that clear and distinct conceivability tracks real metaphysical possibility. Antoine Arnauld, in the Fourth Objections, surfaced exactly this and attacked it: I can clearly and distinctly conceive of a right-angled triangle without knowing the Pythagorean theorem holds of it, and that doesn't make the theorem contingently false of that triangle. Conceiving two things apart, clearly, doesn't obviously licence a claim about what's really separable in the world. Naming the assumption is the whole of Arnauld's objection, he doesn't dispute the cogito at all.

How to run it

1. Present your reasoning, not your conclusion. Premises hide in the steps.
2. Ask what's being relied on but not stated.
3. For each surfaced premise, ask: is this a claim most people in the debate would grant, or is it exactly what the two sides disagree about?
4. Test the load-bearing ones: if this premise is false, does the conclusion survive?
5. State the important ones explicitly in your essay. A stated, defended premise is a strength. An unstated one is where a marker will push.

Here is my argument: [paste]. Don't tell me if I'm right. List the premises I'm relying on but haven't stated. For each one, tell me whether it's a premise most people in this debate would grant, or whether it's actually the thing the two sides disagree about.

Across traditions

Nagarjuna's Mulamadhyamakakarika runs this method systematically against claims of inherent, independent existence (svabhava). His characteristic move on any claim, does a thing arise from itself, from another, from both, or from neither, is a fourfold surfacing of the metaphysical commitment hiding inside ordinary talk about motion, causation and selfhood, followed by showing that commitment leads to contradiction on every branch. The target is always the same kind of thing Arnauld found in Descartes: an assumption treated as too obvious to need stating, examined only once someone insists on stating it.

Pitfalls

1. Confusing assumptions with errors. Most surfaced premises are choices, and many are defensible once named.
2. Surfacing trivia. Ask for the load-bearing ones, not every implicit claim in the passage.
3. Stopping at the list. The survives-if-false test is the actual method.
4. The tell: every premise surfaced is one you'd already have named without help. Give your real reasoning, not a tidied version, or the exercise finds nothing.

Try this today

Take the last paragraph of philosophical argument you wrote. Paste it and ask only: what am I assuming here that I haven't said? Then ask whether that assumption is one your own school of thought treats as obvious, or whether it's exactly what's disputed between schools.