Logic and Scientific Thinking

Persuasion and Rhetoric

Bogdan G. Popescu

bgpopescu@tec.mx

Tecnologico de Monterrey

Welcome

Learning Outcomes

Trace how a message moves a mind: attention → trust → feeling → conclusion.

Name the appeals’ honest and counterfeit forms — ethos · pathos · logos.

Sort the senders behind the same machine — and apply the three questions.

Recap

Question	Answer from the previous session
Misinformation?	False premises — the wrong number, not the wrong link
The gallop?	Volume that hides false premises and missing links
The defense?	One claim, its evidence — and inoculation

Previously we asked: who floods on purpose? First, a deeper puzzle: how does a message persuade at all?

The Puzzle

“Youth and Inexperience” — Reagan vs. Mondale (1984)

One sentence, zero direct evidence — and watch the other podium.

The Puzzle

The question	“You are already the oldest president in history… Kennedy went days without sleep in the Cuban Missile Crisis. Could you function?”
The answer (Reagan)	“I will not make age an issue… I am not going to exploit my opponent’s youth and inexperience.”
The result	The hall laughs — opponent laughs — the question isn’t pressed again that night.

The question was legitimate;
The reply gives no direct evidence — yet you will find an argument in it later
The reply left no opening for the moderator or the opponent to press on

Today’s question: how can a reply persuade without answering?

The Process

The Three Filters

Step one of the answer: a claim must pass three filters inside each listener before it becomes opinion:

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flowchart LR
  M["a claim arrives<br/>(news, ad,<br/>rumor, post)"] --> F1["FILTER 1: ATTENTION<br/>does it reach<br/>you at all?"]
  F1 --> F2["FILTER 2: IMPRESSION<br/>how does it land?<br/>fast, automatic"]
  F2 --> F3["FILTER 3: FIT<br/>your beliefs,<br/>your group"]
  F3 --> P["added to your<br/>stored ideas"]
  P -- when asked --> O["your answer:<br/>ideas at hand"]
  A1["most claims stop here<br/>topic interest<br/>raises the odds"] -.-> F1
  A2["confident sounds right<br/>repeated feels true<br/>feeling comes first"] -.-> F2
  A3["agreeable claim:<br/>can I believe it?<br/>disagreeable claim:<br/>must I believe it?"] -.-> F3
  style A1 fill:#f3ded9,stroke:#b44527,color:#b44527
  style A2 fill:#f3ded9,stroke:#b44527,color:#b44527
  style A3 fill:#f3ded9,stroke:#b44527,color:#b44527
  style O fill:#cfe0d8,stroke:#4a7c6f

Mechanisms: fast-vs-slow thinking (Kahneman 2011) · shortcut persuasion (Petty & Cacioppo 1984) · motivated reasoning (Kunda 1990; Gilovich 1991). Storage, sampling, and topic awareness: Zaller (1992) — his terms: reception, acceptance, “considerations,” “sampling.”

When Opinions Change

The same three filters decide it — an opinion moves only when a challenge gets through:

	Opinion stays when…	Opinion can move when…
Attention	the challenge never reaches you	you meet the other side’s actual case
Impression	the messenger is distrusted	a source you already trust says the unexpected
Fit	your group’s position is at stake	identity stakes are low — or the case is framed in your values

Change is usually gradual: new stored ideas shift the mix your answers are drawn from (Zaller 1992).

Change earned by argument lasts; change won by shortcuts fades (Petty & Cacioppo 1986).

The Three Appeals

Ethos · Pathos · Logos

Rhetoric — “the faculty of observing, in any given case, the available means of persuasion” (Rhetoric I.2, 1355b).

In plain terms: whatever the topic, notice everything that could move this audience.

Aristotle’s Rhetoric — the first map of persuasion:

Ethos — trust in the speaker: credibility, authority.
Pathos — the feelings of the audience.
Logos — the argument: premises and links.

Persuasion always mixes all three:

the fallacy families are these appeals abused

Raphael, The School of Athens (detail, c. 1510) — Plato in gray, Aristotle in color. Public domain.

Ethos

The question it answers: “why should I listen to you?”

Borrowed trust: the white coat, the title.
Performed trust: sounding confident and composed.
Relational trust: “I’m one of you.”
Counter-ethos: make the other side untrustworthy.

Trust opens every filter — it decides whose evidence even gets heard.

Pathos

The question it answers: “what should matter to me right now?”

Each emotion is a hidden claim:

Fear: “the danger is near.”
Anger: “someone is to blame.”
Pity: “someone needs help.”
Pride: “this is what we do.”
Humor: “relax — we’re friends here.”

Logos

The question it answers: “why does this seem to follow?”

The honest version: valid form, true premises — the ladder.
The persuasive shortcuts: stories · examples · numbers · framing.
The oldest trick: leave a gap — the listener fills it (enthymeme).
What you conclude yourself, you rarely doubt.

The counterfeit: sounds like reasoning, offers no checkable claim — “studies show…”

The Instruments, Used and Abused

Every appeal has an honest use — the trouble is persuasion “through rhetoric alone” (Vaughn 2019):

The appeal	Used honestly	The counterfeit
Ethos — “trust me”	a cardiologist shows how she knows	the rented white coat in an ad
Pathos — “feel this”	a real danger — plus what to do	fear or pity doing all the work
Logos — “it follows”	reasons you can check, step by step	“studies show…” — which studies?

Where Does It Outrun?

A councillor speaks at a public meeting:

“I ran this district’s emergency room for eleven years. Last winter we admitted 63 children for respiratory illness — up from 24 the winter before. I have sat with those parents. The council must fund the new clinic.”

1. Which appeals are here — and is any of them dishonest?

2. Where exactly does the persuasion outrun the evidence?

Answers — First, Standard Form

Strip the delivery away and write the argument out, the way you have done since Session 2:

P1.	Child admissions for respiratory illness rose from 24 to 63 last winter. (E)
P2.	(hidden) That rise is a problem the council should act on. (N)
P3.	(hidden) Funding the new clinic would reduce it. (E)
C.	The council must fund the new clinic.

P1 she gave you. P2 you granted without noticing. P3 was never stated and never supported — and the conclusion rests on it.

Answers — Where the Appeals Land

Now put the three appeals back on, and see which line each one supports:

Ethos — eleven years running the emergency room	supports P1 — why you believe her number
Pathos — “I have sat with those parents”	supports P2 — why the rise counts as a problem
Logos — 63 against 24	is P1 — specific, sourced, checkable

P3	nothing. No appeal, no evidence, no mention

Every appeal is legitimate. Every one of them lands on a premise she already had. The gap is the one line nobody argued for.

So the general test is: what is claimed, what supports it — and does that support warrant that conclusion?

NARRATION: The table shows you where each appeal lands, so let me give you what it cannot. Every appeal here is legitimate, and every single one attaches to a premise she could already defend. Premise three gets nothing. That is why question one has no satisfying answer: there was never a fake appeal to find. Here is the failure, in three short steps. She proved one thing. She concluded a different thing. The proof was real, it just belonged to the other claim. That is far more common than counterfeit rhetoric and much harder to catch, because everything you stop and check comes back clean. That line at the bottom is the general shape of the test: what is claimed, what supports it, and whether that support warrants this conclusion. Hold on to it, because at the end of the session we compress it into three questions you can run at conversational speed.

Working Together

Interlocking Appeals

The appeals aren’t three separate scores — each changes the others:

Trust someone → you believe their numbers. (ethos → logos)
Fear something → its facts feel bigger. (pathos → logos)
A good argument → “she’s smart.” (logos → ethos)
A shared laugh → “he’s one of us.” (pathos → ethos)
Hear it often → it feels familiar — and familiar feels true.

So don’t judge a message one appeal at a time — trace the sequence.

The Joke, Retraced

The opening puzzle — retraced with the tools you now have:

1. Attention	The oldest president is asked, point-blank: can you function?
2. “Trust me” (ethos)	The joke shows composure — not the stamina the question asked about.
3. “Feel this” (pathos)	Humor: “relax, we’re friends” — the hall laughs, even Mondale.
4. “It follows” (logos) — the premise you supply	“A man this calm under fire has stamina to spare.”
5. What would decide it	Actual evidence of stamina — which the joke never gave.

The puzzle, solved: the reply didn’t argue — it made you build the argument.

The habit to keep: after the laugh, ask — was the question answered?

NARRATION: Now the puzzle, solved. The question got attention. Then the joke showed composure, and here is the part to be precise about: composure is not what the question asked about. The question asked whether he could function without sleep. Composure is the quality next door, and that small distance is exactly where you did the work. The humour made the room friendly, and Mondale laughed too, which cost him the moment. Then look at the row about the premise you supply, because it is the important one. Nobody stated any argument, so you built it yourself, and the slide gives you the line you built: a man this calm under fire has stamina to spare. Calm under fire just means calm when the pressure is on. That is the argument Reagan never made, and because you made it, you never questioned it. So keep one question for after the laugh. Was the question answered?

Whose Hands?

Ignorance vs. Intent

The claim returns — “the cafeteria scored 42” — from two very different senders:

	shared believing it	spread knowing it’s false
The name	misinformation	disinformation
The failure	an honest bad premise	a deliberate lie

Working definitions — fields draw these lines differently.

Fallacies and floods, used deliberately, are tools to gain power.

The same catalogue shows exactly how these tactics work — learning it is the defense.

Indifference to Truth

The third sender never opened the report — said 42 because it worked (Frankfurt 2005):

	relationship to truth
The honest speaker	tries to describe reality accurately.
The liar	knows the truth matters — and works to conceal it.
The bullshitter	says whatever works; truth is incidental.

The diagnostic: is the speaker trying to establish the truth, conceal it — or just produce an effect?

The guard: a false claim doesn’t prove lying — and a true one doesn’t prove care.

The Defense

Three Questions

Everything today distills into three habits:

Was the question answered?
What did it actually prove — is there a checkable claim?
Which premise did you supply?

Ask them after the charm has worked — that is the discipline.

Who Checks You?

The joke worked because you built the argument. So — who checks it?

You? Weakest — everyone finds their own reasoning convincing.
A friend who agrees? Weak — agreement supplies no resistance.
Someone who disagrees? Better — but only under one condition.

The evidence: alone, about 1 in 10 people solve a logic puzzle — arguing it out in a group, 8 in 10 (Mercier & Sperber 2017).

The condition: they must share your goal of getting the answer right.
An opponent who only wants to win produces heat, not checking.

The last defense: say your reasoning out loud to someone willing to challenge you — who wants the right answer as much as you do.

Exercise — The Dissection

In pairs — pick one specimen:

1. “You’re not you when you’re hungry.” (a chocolate ad)

2. “Trust me — I’ve used it for years, and it changed my life.” (an influencer)

3. “Everyone is switching — don’t be the last.” (a phone ad)

Your task: fill the joke’s five rows for your specimen — attention · trust me · feel this · the premise you supply · what would decide it.

Debrief: which specimen carried the least argument — and persuaded the most?

The Dissection — Answers

1. “You’re not you when you’re hungry.” (chocolate)

Attention	The absurd transformation — a friend becomes a diva.
“Trust me”	Brand familiarity only. Nobody vouches for anything.
“Feel this”	Humor: relax, we’re friends.
The premise you supply	Hunger makes me not myself → this bar fixes hunger → buy it.
What would decide it	Would any snack do the same?

2. “Trust me — I’ve used it for years, and it changed my life.” (influencer)

Attention	Direct address, a face you already follow.
“Trust me”	The strongest row: I’m one of you — and zero credentials, often an undisclosed payment.
“Feel this”	Aspiration — changed my life sells a future self.
The premise you supply	It worked for them, so it will work for me.
What would decide it	What changed, measured how — and were they paid to say it?

3. “Everyone is switching — don’t be the last.” (phone)

Attention	Urgency — don’t be the last.
“Trust me”	The crowd as the authority — bandwagon is relational ethos at scale.
“Feel this”	Pride and fear of being left out, in one clause.
The premise you supply	If everyone is switching, it must be better.
What would decide it	Is it actually better? A count of buyers is not a measure of quality.

Each one could be decided — the last row says how. None of them offers the evidence that would decide it.\ And the specimen carrying the least support usually persuades the most.

Conclusion

How does a message move a mind?

Persuasion begins by winning attention.
Ethos decides whom we trust; pathos, what feels urgent.
Logos supplies the path — sometimes genuine, sometimes counterfeit.
The same techniques serve the honest, the mistaken, the liar, the indifferent.
The defense: three questions — answered? · proved? · which premise was yours?

Homework: find one ad or speech — trace the sequence, then run the three questions.

References

Aristotle. Rhetoric. (any scholarly edition)
Frankfurt, H. G. (2005). On bullshit. Princeton University Press.
Gilovich, T. (1991). How we know what isn’t so: The fallibility of human reason in everyday life. Free Press.
Kahneman, D. (2011). Thinking, fast and slow. Farrar, Straus and Giroux.
Kunda, Z. (1990). The case for motivated reasoning. Psychological Bulletin, 108(3), 480–498.
Mercier, H., & Sperber, D. (2017). The enigma of reason. Harvard University Press.
Petty, R. E., & Cacioppo, J. T. (1984). The effects of involvement on responses to argument quantity and quality: Central and peripheral routes to persuasion. Journal of Personality and Social Psychology, 46(1), 69–81.
Petty, R. E., & Cacioppo, J. T. (1986). The elaboration likelihood model of persuasion. In L. Berkowitz (Ed.), Advances in experimental social psychology (Vol. 19, pp. 123–205). Academic Press.
Vaughn, L. (2019). The power of critical thinking: Effective reasoning about ordinary and extraordinary claims (6th ed.). Oxford University Press.
Zaller, J. R. (1992). The nature and origins of mass opinion. Cambridge University Press.