Logical Fallacies

LogFall

A practical logical-fallacies reference with clear explanations, usable examples, and teaching tools.

Fallacy profile

Begging the question

Occurs when an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises.

Formal

Definition

Occurs when an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises.

Illustrative example

This source is trustworthy because it tells the truth, and we know it tells the truth because it is a trustworthy source.

Teaching gauges

These 0-100 gauges are teaching aids for comparing fallacies. They are editorial classroom estimates, not measured statistics.

Very common

80

Common in today's rhetoric

Appears regularly in everyday public rhetoric.

Hard to spot

30

Easy to spot

Hard to see without slowing down and reconstructing the reasoning.

Very easy to slip into

80

Easy to innocently commit

A frequent unintentional slip in ordinary reasoning.

Foundational

25

Difficulty

Usually approachable without much prior logic background.

Middle school+Formal logic

Reference

Family

Formal/Structural Fallacy

The argument fails because its internal structure does not validly carry the premises to the conclusion.

Aliases

petitio principii

Quick check

If the premises were true, would the conclusion still fail to follow?

Why it misleads

A fuller explanation of how the fallacy works and why it can look persuasive.

Circularity can be obvious, but it is often hidden behind rewording, loaded descriptions, or a chain of claims that loops back to the start. The argument feels like support has been offered when the conclusion has only been restated.

That's like saying...

Instead of leading with the label, this analogy answers the shape of the reasoning move directly so the mistake is easier to see in plain language.

Fallacious claim

This source is trustworthy because it tells the truth, and we know it tells the truth because it is a trustworthy source.

That's like saying...

That's like using your own house key as proof that you deserve to be inside. The conclusion is being smuggled back in as if it were independent support.

Caveat

This label is easy to overuse. The point here is not to call every weak argument by this name, but to reserve it for the exact misstep it describes.

Common misapplication

Do not use this label as a synonym for raising a question or sounding circular. It applies only when the conclusion is already being assumed inside the support for the conclusion. Circularity can be obvious, but it is often hidden behind rewording, loaded descriptions, or a chain of claims that loops back to the start.

Use the label only when...

Use this label only when an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises. If the real problem is that a syllogism tries to draw a positive conclusion even though one of the premises is negative in a way that cannot support that conclusion, the better label is Affirmative conclusion from a negative premise.

Often confused with

These near neighbors are easy to mix up, so use the comparison to see the exact difference.

Comparison

Affirmative conclusion from a negative premise

Why people mix them up: Both often look like formal mistakes at first glance.

Exact difference: Begging the question happens when an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises. Affirmative conclusion from a negative premise happens when a syllogism tries to draw a positive conclusion even though one of the premises is negative in a way that cannot support that conclusion.

Quick split: If the premises were true, would the conclusion still fail to follow? Then compare it with If the premises were true, would the conclusion still fail to follow?

Comparison

Affirming a disjunct

Why people mix them up: Both often look like formal mistakes at first glance.

Exact difference: Begging the question happens when an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises. Affirming a disjunct happens when someone treats an ordinary 'or' as if it were exclusive and concludes that one option must be false because the other is true.

Quick split: If the premises were true, would the conclusion still fail to follow? Then compare it with If the premises were true, would the conclusion still fail to follow?

Visual argument map

This map highlights the gap between the stated structure and the conclusion the argument tries to force.

Premise pattern

This source is trustworthy because it tells the truth, and we know it tells the truth because it is a trustworthy source.

Invalid step

The structure fails when an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises.

What the premises still allow

Circularity can be obvious, but it is often hidden behind rewording, loaded descriptions, or a chain of claims that loops back to the start. The argument feels like support has been offered when the conclusion has only been restated.

What a valid repair needs

If the premises were true, would the conclusion still fail to follow?

Practice And Repair

Extra teaching tools that show why the fallacy is persuasive, what to look for, and how to correct it.

Why it matters

Why this mistake matters

Begging the question threatens rationality because an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises.

Main reasoning problem

An argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises.

Why this kind of mistake matters

It gives a conclusion the feel of deductive force even when the structure does not license it.

Check yourself

The assessment area now uses mixed 10-question sets, so the fallacy is not announced in the title before the quiz begins.

What the assessment does

You will work through a mixed set of fallacy-identification questions. Focused links from a fallacy page will quietly include this fallacy among nearby look-alikes without announcing the answer in the page title.

Questions to ask

Use these category-based prompts to audit similar arguments.

Prompt 1

If the premises were true, would the conclusion still fail to follow?

Case studies

Each case study explains why the example fits the fallacy and links back to its source whenever source information is available.

How an unsubstantiated, anonymous affidavit about the ABC presidential debate was amplified online

PolitiFact's September 20, 2024 reconstruction of the fake ABC whistleblower affidavit is especially valuable because it shows how public figures shared the claim while conceding they did not know whether it was true. That is a live, well-documented case of conjecture and amplification outrunning authentication. The fallacy here is Begging the question: an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises. That matters here because circularity can be obvious, but it is often hidden behind rewording, loaded descriptions, or a chain of claims that loops back to the start. A better analysis would remember that the argument feels like support has been offered when the conclusion has only been restated.

PolitiFact · 2024-09-20

Conspiracy-style reasoning often treats the absence of confirming evidence as proof that the conspiracy is powerful enough to hide the evidence, which assumes the conclusion inside the explanation. The fallacy here is Begging the question: an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises. That matters here because circularity can be obvious, but it is often hidden behind rewording, loaded descriptions, or a chain of claims that loops back to the start. A better analysis would remember that the argument feels like support has been offered when the conclusion has only been restated.

Debates about 'real journalism' or 'real science' sometimes define the trustworthy outlet or institution as whichever one already agrees with the speaker's preferred view. The fallacy here is Begging the question: an argument quietly assumes the very point it is supposed to prove, so the conclusion is built into the premises. That matters here because circularity can be obvious, but it is often hidden behind rewording, loaded descriptions, or a chain of claims that loops back to the start. A better analysis would remember that the argument feels like support has been offered when the conclusion has only been restated.

Related fallacies

Nearby entries chosen by shared categories and family resemblance.