Lesson 2 · How Not to Commit Every Fallacy in the Book

Recognising bad reasoning without replacing argument with accusations of fallacy.

Estimated study time: 40–50 minutes · Stage I: Foundations of Reasoning

Before we begin

A fallacy is a defect in reasoning. It isn't a magic word that makes an opponent wrong, nor is it a personal insult. The purpose of learning fallacies is to recognise what goes wrong in an argument and, where possible, correct it.

You will encounter fallacies on both sides of religious debate. Some Christian apologists manufacture imaginary atheist positions; some atheists mock caricatures of Christian doctrine. Neither practice becomes respectable because the person committing it is on your side.

Working rule: diagnose the defective inference, not merely its label. Say precisely why the conclusion isn't supported.

1. Straw men: arguing against an invention

A straw man substitutes an easier, less plausible version of a position for the one an opponent actually holds.

"Atheists believe that everything came from nothing, by nothing, for no reason."

Atheism, minimally understood, is the absence of belief in gods; it doesn't by itself entail any particular cosmology. Some atheists hold naturalistic accounts of cosmic origins; others suspend judgement. A person might believe in an eternal universe, a finite universe with an unresolved origin, or a physical model in which conventional temporal language breaks down. To refute a position, you must first identify one somebody actually defends.

Repair: ask your interlocutor to state their position, then reproduce it in terms they would recognise. If the argument concerns a particular cosmological model, name that model and criticise its claims rather than assigning it to every atheist.

The same duty applies in reverse. Atheists should not assume that all Christians believe God is an elderly man sitting above the clouds, or that Aquinas thought everything, without exception, must have a cause.

2. Begging the question and circular reasoning

An argument begs the question when the premises assume, explicitly or covertly, the very point in dispute. Circular reasoning is a particularly obvious form.

"The Bible is true because it is the word of God; we know it is the word of God because the Bible says so."

That reasoning offers no independent support to someone who doesn't already accept biblical authority. It may function within an existing devotional framework, but it cannot by itself establish the authority in dispute.

Repair: provide independently accessible reasons to believe the relevant claim, or openly state that the argument is internal to a faith tradition rather than an independent proof.

Not every argument using a premise that the listener doubts is circular. The diagnosis depends on whether the premise is supported independently or simply repeats the conclusion in disguise.

3. Equivocation: changing meanings mid-argument

Equivocation occurs when a crucial term changes meaning during an inference.

"The universe follows laws. Laws require lawmakers. Therefore the universe requires a divine lawmaker."

In the first sentence, "laws" refers to descriptive regularities or mathematical formulations of natural behaviour. In the second, "laws" are prescriptions imposed by a legal authority. The inference slides from one meaning to another.

Repair: define law consistently, then supply a separate argument that natural regularities require agency. You may attempt that argument, but you cannot obtain it by swapping dictionary senses.

Other ambiguous words in theological debate include nothing, cause, faith, theory, random, information, design, objective and free. Many arguments dissolve as soon as their central terms are defined.

4. False dilemmas: pretending there are only two choices

A false dilemma excludes relevant alternatives without justification.

"Either God created life or it arose by pure accident."

This excludes possibilities such as natural processes involving both law-governed chemistry and contingent historical events. Evolution by natural selection, for example, isn't adequately described as "pure accident". The origins of life and the diversification of life are also distinct scientific questions.

Repair: identify the actual explanatory alternatives and show why the ones you reject are inadequate. An argument gets stronger by eliminating alternatives with evidence, not by ignoring their existence.

A dilemma may be legitimate if its alternatives are genuinely exhaustive: "Either proposition P is true or not-P is true" is exhaustive in classical logic. The problem is not presenting two possibilities; it is pretending two selected possibilities exhaust a wider field.

5. Affirming the consequent

Recall the pattern:

If P, then Q. Q. Therefore P.

This is not generally valid. If a creator designed the cosmos, some forms of order might be expected. But the observation of order doesn't establish creation unless competing explanations are addressed and the evidential relationships are properly argued.

"If God exists, people can have profound religious experiences. People have profound religious experiences. Therefore God exists."

Religious experiences are real experiences. What remains in question is their cause and interpretation. A serious argument would consider whether the experiences are more probable under theism than under relevant alternatives.

Repair: shift from a spurious deduction to an explicitly comparative evidential argument, if the available evidence supports one.

6. Burden shifting and arguments from ignorance

"You can't prove God doesn't exist, so God exists."

An inability to establish not-P doesn't establish P. Equally, "You can't prove God exists, so God doesn't exist" fails as a deduction.

Claims carry justificatory responsibilities. The burden of producing evidence falls on whoever proposes a particular proposition, although both parties may make claims requiring support. A person who merely withholds assent need not demonstrate the negation of every proposition presented to them.

Repair: state what you claim and the reasons that support it. Don't demand that scepticism do the work of your own argument.

7. Appeals to authority: useful evidence or misused prestige?

There is nothing inherently irrational about consulting qualified specialists. Much ordinary knowledge depends on credible testimony and expertise. The mistake is to treat a person's prestige as a guarantee, particularly outside their field.

"A Nobel laureate believes in God, so God exists."

A laureate's achievement in physics, chemistry or another discipline doesn't establish expertise in metaphysics. Even a specialist philosopher's conclusion must be assessed by the arguments offered.

Repair: cite the expert's relevant reasoning and evidence, ideally corroborated by independent specialists. Don't substitute a famous name for the argument it allegedly supports.

8. Genetic fallacies, ad hominem and motive speculation

The genetic fallacy rejects a claim solely because of its origin. An ad hominem attacks a person in place of engaging with their argument.

"You only reject God because you want to sin."

Even if a person's motives were known, motives alone wouldn't establish whether their conclusion is true. The assertion additionally presumes access to another person's internal psychology.

Likewise, "That argument came from a pastor, so it must be false" is poor reasoning. The argument must be examined on its merits.

There are legitimate exceptions: evidence of dishonesty, a conflict of interest, or a source's poor track record can matter to the credibility of testimony. But that differs from proving a proposition false merely by insulting its speaker.

9. The fallacy fallacy

One of the most important corrections in this lesson is that a bad argument for P doesn't entail that P is false.

"Your argument for God is circular, therefore God doesn't exist."

That conclusion doesn't follow. The circular argument fails as a justification. The underlying proposition remains a separate question.

Repair: state the limited conclusion you've actually established: "This argument doesn't give us sufficient reason to accept P." Additional reasoning is needed to conclude not-P.

10. The principle of charity and steelmanning

When an argument is vague, first try to reconstruct its strongest plausible version without quietly supplying controversial premises as though they were established facts.

A good steelman preserves the opponent's intended claim, identifies explicit and hidden premises, and offers the most defensible interpretation available. It doesn't produce a completely different argument and attribute it to the original speaker.

For example, replace "everything has a cause, so God" with a carefully formulated cosmological argument where appropriate. But don't pretend that defending the possibility of a cosmic cause automatically defends the Christian Trinity. Each inference remains accountable.

A useful test: ask, "Would a knowledgeable defender of this position recognise the argument I have reconstructed?" If not, revise it before attacking it.

Worked argument clinic

Original post: "Atheists are just afraid of God. They believe the universe created itself from nothing and have no objective morals. Therefore Christianity is obviously true."

Diagnosis: "Afraid of God" is speculation about motives. "Believe the universe created itself from nothing" is an unsupported generalisation about atheists. "Have no objective morals" is another unsupported claim. None of these, individually or together, logically establishes Christianity.

Charitable reconstruction: A more sophisticated defender might argue that contingent reality requires a necessary explanation, or that objective moral facts are best explained by a personal moral foundation. These are recognisable philosophical arguments. Both require independently defended premises, and neither by itself establishes specifically Christian doctrine.

The improved discussion: Select one argument, define its crucial terms, present the premises, defend them and assess substantive counterarguments. The result is slower, but capable of making intellectual progress.

Practice exercises

1. "Science uses theories; theories are guesses; therefore evolution is only a guess." Identify the key mistake.
2. "Either you agree with my interpretation of Genesis or you call God a liar." What alternatives are being excluded?
3. "A famous neuroscientist believes miracles happen, so this particular miracle happened." What's missing?
4. "Your argument for the Resurrection fails; therefore the Resurrection never happened." Diagnose this inference.
5. Reformulate one accusation of fallacy into a sentence that explains why the original inference fails.

Lesson summary

• A fallacy is a problem in reasoning, not proof that the speaker is stupid or malicious.
• Straw men, equivocation, false dilemmas and circular arguments are especially common in online religious disputes.
• Famous supporters and sincere experiences may be relevant evidence, but they aren't self-validating proofs.
• Criticising a failed argument doesn't establish the opposite conclusion.
• Reconstruction and charity make criticism stronger, not weaker.

Further reading: OpenStax, Introduction to Philosophy, chapter 5 and Stanford Encyclopedia of Philosophy, Fallacies.