Enthymemes: Arguments with a Premise Left Unsaid
Many real-life arguments are incomplete on the page but still feel persuasive in conversation. An enthymeme is an argument that leaves out a needed assumption (a missing premise) that must be supplied for the stated reason(s) to support the conclusion.
Speakers omit premises for several common reasons: they assume the audience already agrees, they want to sound concise, or the missing step feels “obvious.” Your job as a careful reasoner is to make that hidden step explicit and then evaluate it.
Why missing premises matter
- They can hide the real point of disagreement. Two people may agree on the stated reason but disagree on the unstated assumption.
- They can smuggle in questionable ideas. The argument may rely on a stereotype, an overgeneralization, or an unrealistic standard.
- They affect strength. If the missing premise is weak or implausible, the whole argument weakens.
The Core Question: “What Must Be True?”
The most reliable way to uncover a missing premise is to ask:
What must be true for the stated reason(s) to support the conclusion?
This question forces you to identify the bridge between the reason and the conclusion. You are not asking what would make the conclusion true in general; you are asking what would make the reason actually support it.
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Step-by-step method to uncover missing premises
- Step 1: Write the argument in a simple layout. List the stated premise(s) and the conclusion.
- Step 2: Look for the gap. Ask what connection is needed between the premise(s) and conclusion.
- Step 3: Propose a missing premise candidate. Phrase it as a claim that, if added, would make the support work.
- Step 4: Test the candidate. Check whether it is (a) necessary, (b) plausible, and (c) charitable without changing the argument’s intent.
A Structured Template You Can Reuse
Use this template to make the hidden structure visible:
Stated premise(s): [P1, P2, ...] → Missing premise candidate: [MP] → Conclusion: [C]Then test the missing premise candidate with three checks:
- (a) Necessary? Without MP, do the stated premises fail to support C (or support it much less)? If the argument still works without MP, it may not be the missing premise you need.
- (b) Plausible? Is MP believable or reasonable in the context? A missing premise can be necessary but still too extreme to accept.
- (c) Charitable (without changing intent)? Choose an MP that makes the argument as strong as it reasonably can be, while still matching what the speaker likely meant. Don’t “rescue” the argument by inventing a different argument.
Everyday Examples of Enthymemes (and How to Fill the Gap)
Example 1: Diet advertisement
Claim: “Try SlimNow. People who use it lose 10 pounds in two weeks. So it works.”
| Part | Content |
|---|---|
| Stated premise(s) | People who use SlimNow lose 10 pounds in two weeks. |
| Missing premise candidate | If people who use SlimNow lose weight, then SlimNow is what caused the weight loss (not something else). |
| Conclusion | SlimNow works (is effective for weight loss). |
Test the missing premise
- Necessary? Yes. Without a causal link, the premise could be a coincidence or due to diet/exercise changes.
- Plausible? Maybe, but it depends. Many other factors could explain weight loss.
- Charitable? Fair: ads usually imply the product is the cause.
Two alternative missing premises (compare):
- MP-A (stronger, less plausible): “SlimNow is the only relevant change users make.”
- MP-B (more plausible, weaker): “SlimNow contributes significantly to weight loss for typical users.”
MP-A makes the argument more decisive but is often unrealistic; MP-B fits real life better but yields a more modest conclusion.
Example 2: Safety warning
Sign: “Caution: Wet floor. Walk slowly.”
| Part | Content |
|---|---|
| Stated premise(s) | The floor is wet. |
| Missing premise candidate | If the floor is wet, walking quickly increases the risk of slipping. |
| Conclusion | You should walk slowly. |
Test the missing premise
- Necessary? Yes. “Wet floor” alone doesn’t logically require “walk slowly” unless wetness raises slip risk.
- Plausible? Yes, generally.
- Charitable? Yes; it matches the warning’s intent (risk reduction).
Two alternative missing premises (compare):
- MP-A: “Any increased risk of slipping is enough to justify walking slowly.”
- MP-B: “The risk is high enough here that walking slowly is the safest reasonable response.”
MP-B is more specific and often more plausible; MP-A is broader and may be too demanding in low-risk situations.
Example 3: Policy claim
Statement: “We should ban phones in class because students get distracted.”
| Part | Content |
|---|---|
| Stated premise(s) | Phones distract students in class. |
| Missing premise candidate | If something significantly distracts students in class, it should be banned in class. |
| Conclusion | Phones should be banned in class. |
Test the missing premise
- Necessary? Yes. Distraction alone doesn’t automatically imply banning; other responses are possible (rules, enforcement, teaching strategies).
- Plausible? It depends. Some distractions are tolerated; bans have costs.
- Charitable? A charitable version should reflect the speaker’s likely goal (improving learning) without turning it into a different policy.
Two alternative missing premises (compare):
- MP-A (too strong): “Anything that distracts students should be banned.”
- MP-B (more charitable): “If an item causes substantial distraction and the educational benefits of allowing it are outweighed by the costs, it should be banned.”
MP-B better matches how policy arguments usually work (balancing costs and benefits) while still supporting the intended conclusion.
How to Avoid Common Mistakes When Supplying Missing Premises
Mistake 1: Adding a premise that changes the argument
If the speaker argues “ban phones,” don’t replace it with “teach better self-control” as the missing premise. That’s a different argument (a counterproposal), not the hidden bridge premise.
Mistake 2: Making the missing premise too specific
Overly detailed premises can “rig” the argument. Example: “Phones distract students in 87% of classes” may not be what the speaker meant. Prefer a general claim that still connects the reason to the conclusion.
Mistake 3: Making the missing premise too moralized or extreme
People often argue with an implicit “should” principle, but it’s rarely absolute. Replace “always” and “never” with more realistic thresholds when charity allows.
Mistake 4: Confusing a missing premise with missing evidence
Sometimes the gap is not an unstated assumption but a lack of support for a stated claim. Example: “SlimNow users lose 10 pounds” might need evidence (data), not a new premise. Missing premises are about the logical bridge, not the proof of a premise.
Mini-Checklist: The Three Tests in Practice
When you propose a missing premise, quickly run this checklist:
- Necessity: If MP were false, would the stated premise(s) still support the conclusion?
- Plausibility: Would a reasonable person in this context accept MP?
- Charity: Does MP strengthen the argument without rewriting it into a new one?
Exercises: Propose Two Assumptions and Compare Them
For each item below, do the following: (1) write the stated premise(s) and conclusion, (2) propose two missing premise candidates (MP-A and MP-B), and (3) decide which is more necessary, more plausible, and more charitable.
Exercise 1: Fitness influencer
“I started drinking green juice every morning, and my energy improved. Green juice boosts energy.”
- Your MP-A: ____________________
- Your MP-B: ____________________
- Compare: Which MP is more plausible? Which one makes the argument stronger? Which best matches what the influencer likely intends?
Exercise 2: Product safety
“Keep batteries away from children because they’re dangerous.”
- Your MP-A: ____________________
- Your MP-B: ____________________
- Compare: Does one MP rely on a specific type of danger (choking, chemical burn, ingestion)? Is that specificity warranted or does it overreach?
Exercise 3: Workplace policy
“We should allow remote work because employees will be happier.”
- Your MP-A: ____________________
- Your MP-B: ____________________
- Compare: Do your MPs assume happiness is the top priority, or do they include a balancing condition (productivity, service quality, fairness)? Which is more charitable?
Exercise 4: Public spending
“The city should build more bike lanes because it will reduce traffic.”
- Your MP-A: ____________________
- Your MP-B: ____________________
- Compare: Does one MP assume people will switch from cars to bikes? Does it assume the reduction is large enough to justify the cost?
Exercise 5: School rule
“Students shouldn’t use laptops in lectures because they multitask.”
- Your MP-A: ____________________
- Your MP-B: ____________________
- Compare: Does one MP ignore benefits (note-taking, accessibility)? Which MP best keeps the speaker’s intent while staying realistic?
Quick Practice: Fill the Template
Rewrite each as: stated premise(s) → missing premise candidate → conclusion.
- “Don’t swim here; there are strong currents.”
- “Choose the extended warranty; repairs are expensive.”
- “Vote for the proposal; it will create jobs.”
