Logic, Rhetoric & Fallacies

1.1 The Anatomy of an Argument

An argument has three parts: premises (the assumed facts), inference (the logical link between them), and conclusion (the claim that follows). Deductive arguments claim certainty: if the premises are true and the logic is valid, the conclusion must be true. Inductive arguments claim probability: specific observations lead to general claims, which can always be overturned by a new counterexample. A third mode, abduction, infers the most likely explanation from incomplete evidence: your car won't start; you infer a dead battery, not sabotage.

The core skill is distinguishing validity (does the conclusion follow from the premises?) from soundness (are the premises actually true?). A valid argument with false premises is logically perfect and completely wrong. In political debate, most bad arguments are valid but unsound: the inference works, but the premises are empirically false, unfalsifiable, or smuggled in without examination.

1.2 The Informal Fallacies

A formal fallacy breaks the logical structure. An informal fallacy leaves the structure intact but introduces an irrelevant appeal, a hidden assumption, or a distorted claim. What follows are the fallacies you will meet most often in political speech, editorial pages, and online discourse. We will examine some real examples taken from President Donald J. Trump's speeches and tweets.

Ad Hominem — Attacks the person, not the argument.

"He's a Mexican. We're building a wall between here and Mexico. The answer is, he is giving us very unfair rulings — rulings that people can't even believe."

—Donald J. Trump, Wall Street Journal interview, June 3, 2016

Judge Curiel (born in Indiana) was presiding over the Trump University fraud case. Trump's argument: the rulings should be dismissed because of the judge's ethnic background, not because of any error in the legal reasoning. Even if the biographical detail were relevant, it would not touch the validity of the rulings. The argument stands or falls on its own merits.

Tu Quoque — Dismisses an argument by claiming the speaker is hypocritical.

Bill O'Reilly: "Putin's a killer."

Donald Trump: "There are a lot of killers. We've got a lot of killers. What do you think — our country's so innocent?"

—Donald J. Trump, Fox News interview with Bill O'Reilly, February 5, 2017

Hypocrisy does not invalidate a claim. A major sub-type is Whataboutism, popular in political discourse to deflect criticism of one's own actions by asserting that the critic is guilty of similar or worse behavior ("BuT WhAt AbOuT WhEn YoU dId It? 🥺").

Straw Man — Distorts an argument into a weaker, more extreme version, then defeats the distortion.

"Make no mistake, if you give power to Joe Biden, the radical left will defund police departments all across America. They will pass federal legislation to reduce law enforcement nationwide. They will make every city look like Democrat-run Portland, Oregon."

—Donald J. Trump, Republican National Convention, August 27, 2020

Biden had explicitly and repeatedly stated he opposed defunding the police—including in a May 2020 interview where he said directly "No, I don't support defunding the police." Trump's version of Biden's position bore no resemblance to Biden's actual position. The antidote is steel-manning (see §1.4).

False Dilemma — Presents two options as the only possibilities.

"We will work with them. They have to go. Chuck, we either have a country, or we don't have a country."

—Donald J. Trump, NBC News interview with Chuck Todd, August 15, 2015

This frames the issue as a simple either–or: deport all undocumented immigrants, or the country stops functioning. It leaves out every realistic alternative in between, like immigration reform, guest worker programs, or more targeted enforcement. Once the choice is reduced to "one extreme measure or total collapse," those options vanish from the conversation. That is the point.

Motte-and-Bailey — A speaker makes a bold, controversial claim (the bailey). When challenged, they retreat to a bland, defensible truism (the motte).

Bailey: "Donald J. Trump is calling for a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what the hell is going on."

—Trump campaign press release, December 7, 2015

Motte: "It's not the Muslim ban. It's countries that have tremendous terror."

—Donald J. Trump, Meet the Press, January 2017

Once the executive order faced legal challenges on First Amendment grounds, the explicit religious framing was quietly dropped. The policy became a "travel ban" targeting specific countries—a much more defensible position. When the courts pushed back on the bailey, the motte appeared. One could challenge the speaker: "Which claim are you actually defending: the strong one or the weak one?", but this can be socially awkward, which is exactly why the move keeps working.

Slippery Slope — Asserts that one step inevitably leads to a catastrophic chain, without demonstrating the mechanism linking each step.

"This week it's Robert E. Lee. I noticed that Stonewall Jackson is coming down. I wonder, is it George Washington next week? And is it Thomas Jefferson the week after? You know, you really do have to ask yourself, where does it stop?"

—Donald J. Trump, press conference, August 15, 2017

The implied chain: remove Confederate statues → next the Founders → then all monuments → then history itself. No mechanism is given for why each step follows from the previous one. This is not always a fallacy. Some institutional ratchet effects are real. But asserting the chain is not the same as demonstrating it. For each step, ask: is there an independent reason this follows from the previous one?

Circular Reasoning — The conclusion is hidden in the premises.

"Any negative polls are fake news, just like the CNN, ABC, NBC polls in the election."

—Donald J. Trump, Twitter, February 6, 2017

The argument protecting his approval ratings had the following structure: I am popular → therefore any poll showing otherwise is fake → the proof that a poll is fake is that it is negative → therefore I am popular. By explicitly defining the opposing evidence ("negative polls") as inherently illegitimate ("fake news"), the conclusion (that his true numbers are good) is baked directly into the premise. It creates an unfalsifiable loop: no valid negative evidence can ever be introduced into the argument, because being negative is the stated criterion for the evidence being invalid.

Appeal to Emotion — Emotion substitutes for evidence rather than accompanying it.

"When Mexico sends its people, they're not sending their best... They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people."

—Donald J. Trump, presidential campaign announcement, June 16, 2015

No statistical evidence was offered. The emotional payload: drugs, crime, rape, was doing the argumentative work that data should be doing. Fear is a legitimate response to genuine threats, but it is not a substitute for evidence about whether a threat exists or how large it is.

Post Hoc Ergo Propter Hoc — Correlation dressed as causation. "After this, therefore because of this."

"Since taking office I have been very strict on Commercial Aviation. Good news — it was just reported that there were Zero deaths in 2017, the best and safest year on record!"

—Donald J. Trump, Twitter, January 2, 2018

US commercial aviation fatalities had been trending toward zero for over a decade before Trump took office. The pattern predates him. He arrived after the trend, not before it. The inference from correlation to causation fails in three ways: a third variable drives both (confounder), the arrow runs the other way (reverse causality), or it's coincidence. There will be more on this in a later chapter.

Gish Gallop — Overwhelming an opponent with a torrent of weak claims faster than they can be refuted.

The September 29, 2020 US presidential debate is a documented case study. Fact-checkers at the Washington Post tallied over 30 false or misleading claims from Trump in 90 minutes on mail-in voting, the economy, COVID deaths, the Green New Deal, Hunter Biden, and more. These claims were delivered faster than any rebuttal could track. Biden's attempts to respond to individual claims left most of the torrent unaddressed. The debate was widely described as unwatchable precisely because it was a gallop by design. Do not attempt point-by-point rebuttal. Address the one or two central claims and name the tactic.

1.3 Rhetoric vs. Logic

Aristotle identified three modes of persuasion: Logos (reason), Ethos (the credibility of the speaker), Pathos (emotion). Legitimate persuasion lets logos carry the load, with ethos and pathos in support. Manipulation inverts this: pathos carries the load, logos is absent or fallacious, and ethos is manufactured through credentials, confidence, or tribal affiliation.

The test: strip away the emotional framing and the speaker's credentials. Does the argument stand on its own? If not, you are being persuaded, not convinced.

Social media platforms are built to reward the wrong end of this spectrum. Emotional content generates more engagement than analytical content; outrage outperforms nuance; tribal signaling outperforms evidence. The platforms are optimizing for clicks, which selects for pathos. The result is an environment where good argumentation is invisible and bad argumentation usually goes viral.

1.4 Steel-Manning

A steel man is the strongest possible version of an opposing argument. A refutation that defeats only a weak version of an argument is worthless; it signals to anyone who holds the opposing view that you haven't understood it. If you cannot articulate the best case for a position you oppose, you probably don't understand the issue well enough to have a justified opinion about it.

1.5 Motivated Reasoning

Motivated reasoning is not a fallacy. It is reasoning toward a predetermined conclusion rather than from the evidence. The goal is to protect a belief, not to find truth. A person committing a fallacy through carelessness can be corrected by pointing it out; a person engaged in motivated reasoning will simply reach for a different tool.

Signs:

Asymmetric skepticism: demanding rigorous proof for claims that challenge your priors, accepting thin evidence for claims that confirm them.
Goalpost-moving: when evidence addresses the objection, the objection quietly shifts.
Attribute substitution: when the argument becomes too strong to defeat, attacking the arguer instead.

1.6 How to Evaluate Any Argument

When you encounter an argument, be it in a policy brief, a speech, or a social media thread, run through this checklist:

Conclusion: What is the actual claim being made?
Premises: What reasons are given? Are there hidden assumptions?
Inference: Does the conclusion actually follow from the premises?
Truth: Are the premises empirically supported, or assumed?
Fallacies: Ad hominem? Straw man? False dilemma? Emotional substitution?
Steel man: What is the strongest version of this argument? Can you defeat that?
Motivated reasoning: Is there asymmetric skepticism? Are goalposts moving?
Beneficiaries: Who gains if this argument is accepted? Not a logical test, but a reliable pointer to hidden premises.