Logical Fallacies in Psychology

Logical fallacies frequently committed by experimental and clinical psychologists:

Denying the Antecedent:

If x, then y.
Not x.
Therefore, not y.

Example 1: “If I am charged by an ethics board, then I did something unethical. I am not charged by an ethics board. Therefore, I did nothing unethical.” This is an illogical conclusion since the therapist might have still acted unethically, despite their not receiving a complaint or being charged.

Example 2: “If a theory is taught in an academic institution, then it has some credibility. It is not taught in an academic institution. Therefore, it has no credibility.” This is a false conclusion, since a theory could be very credible, but perhaps so ‘new,’ that it has yet to be integrated into a teaching program.

Affirming the Consequent:

If x, then y.
Therefore, x.

Example 1: “Good clinicians have lots of clients. I have lots of clients, so I must be good.” A clinician may have lots of clients due to their advertising, not their competence.

Example 2: “If Stephen Pinker is an expert in the philosophy of mind and human neuroscience, then he will have a lot to say about the human mind. Pinker has a lot to say about the human mind. Therefore, he must be an expert in the philosophy of mind and human neuroscience.” Though the first 2 premises might be true on their own, the conclusion is clearly false.

Composition Fallacy:

Assuming something true of a part of a whole, must also be true of the whole.

Example 1: “Atoms are invisible to the naked eye. Humans are made up of atoms. Therefore humans are invisible.”

Example 2: “The lower reaches of the nervous system contain modular mechanisms. Therefore the higher levels of the nervous system must also be modular.”

Division Fallacy:

Assuming members of a group possess characteristics of the group

Example 1: “Our human history is plagued by war and violence. Each person must have an instinct or drive toward violence.”

Example 2: “The University makes a lot of money. Each professor working there must earn a large income.”

Golden Mean Fallacy:

Assuming that the most valid conclusion will involve a compromise between two competing positions.

Example: “The behaviorists think that the mind is mostly domain-general in composition. The evolutionary psychologists think that the mind is mostly domain-specific in composition. Therefore, the best theory is one where the mind is half domain-general and half domain-specific in composition.” This sounds like a nice compromise, but it may not reflect the biological realities of our human nature/nurture.

Appeal to Ignorance Fallacy:

Assuming that since there is insufficient evidence establishing that x is false, then x must be true.

Example 1: “Though there are a lot of critics of Jungian theory, no one has conclusively disproven its claims, therefore it must be true.”

Example 2: “In my 4 years practicing therapy, I have never had one complaint or lawsuit suggesting that I am incompetent. Therefore, I must be competent.”

False Dichotomy:

Assuming that there are only two options to choose from, when additional alternatives exist.

Example: “If you do not believe in a genetically pre-programmed model of the human mind, then you must be a ‘blank-slate’ behaviorist or cultural determinist.”

Post Hoc Fallacy:

If x precedes y,
Then x must have caused y.

Example 1: “A therapist decides to try ‘dream therapy’ with one of his regular clients. At the start of the next session, the client reports that they are feeling better. Dream therapy must have helped the client to feel better.” There could have been a number of variables that led to a change in this client’s mood.

Red Herring:

The red herring fallacy involves introducing an irrelevant topic or idea in an effort to distract or lead away from the initial argument. The interlocutor thus evades engaging in rational argumentation related to the main topic of contention.

Example: “You seem to argue that psychology professors should be helping students develop their deductive reasoning skills in the classroom, however, psychology is a social science and does not work in the same way as philosophy.” The argument seems to be about whether we should teach deductive reasoning in our science classes, but the debater wants to change the topic to an argument about whether psychology works in the same way as philosophy.

Ad Hominem:

This fallacy attempts to discredit an argument by attacking the person making it (thus avoiding logical engagement of the evidence or arguments being made).

Example: “Many of your arguments against Social Darwinism or evolutionary psychology are the same as those presented by Steven Jay Gould. But Gould criticized Morton for his ‘mismeasure of man’ and turned out to be a hypocrite, since there were mismeasures and biases in his own work.”

Straw Man/Person:

This fallacy involves mischaracterizing an opponent’s argument or position in a way that makes it sound weak, incoherent, or false.

Example: “You seem to place a larger emphasis on learning, experience, or culture, essentially arguing that the brain is made out of silly putty! So please explain, how does your wad of silly putty become shaped, when the environment is so complex, and there is no internal structure to guide it toward relevant stimuli?”

Naturalistic Fallacy or the ‘is-ought’ problem:

Trying to describe what is ‘good’ within some natural property, or, trying to argue that because something ‘is,’ assuming that it ‘ought’ to be that way. The naturalistic fallacy is a problem because what is ‘good’ is arguably subjective and unidentifiable; it is not clear that what is ‘natural’ is necessarily ‘good.’

Example: “Aggression is a natural impulse or urge in humans. Therefore it is good for us to vent aggressive energy from time to time.”

False Analogy:

Involves a misleading comparison that usually takes the following form:
Object A has quality P and Q.
Object B has A’s quality P.
Therefore Object B must also have A’s quality Q.

Example: “The mind transmits energy and information like a computer. Just like a computer is pre-programmed with computer software, the mind must also be pre-programmed with psychological software that was naturally selected.”

Begging the Question:

A type of ‘circular reasoning’ where the truth of the conclusion is assumed – usually by ‘smuggling’ an assumption that affirms the conclusion, into one or more of the premises.

Example 1:
The human mind and its products are biologically based.
If they are biologically based, they are evolved and innate.
The mind is thus an evolved organ and human behavior is innate.

Example 2:
Jan: God exists because it is written in the Bible.
Bob: Why do you believe what is written in the bible?
Jan: Because it was written by God.

Appeal to Authority:

Assuming that since someone is an ‘authoritative expert,’ then we should believe the claim without having to judge the merits of the argument itself. This fallacy is most obvious when the ‘expert’ is speaking outside of their specific area of knowledge.

Example: “Richard Dawkins is a zoologist that is an expert in neo-Darwinian evolution and has sold millions of books worldwide. Therefore, his arguments about the harms of religion have significant merit and are likely to be correct.”

Poisoning the well fallacy:

A person presents unfavorable information about either an opposing view or the person presenting that view, with the intent of discrediting the other side or ‘polluting’ its argument, making it more likely that it will be dismissed by those who would later hear it.

Example 1: Do not listen to him/her! Remember, he/she smoked pot when they were in university!

Example 2: Many of the people who are about to speak here are atheists – they deny God. But without God, they have no morals. Therefore, they should not be trusted.

Reification Fallacy:

Involves treating an abstract, hypothetical construct, as if it were a concrete or physically real phenomenon. It essentially involves us regarding our psychological constructs as ‘real things.’

Example 1: “This person’s low IQ score indicates that their brain is less developed.” IQ is a construct, and not a ‘real thing.’ We cannot make inferences about human brains from such constructs.

Example 2: “The human mind is made up of adaptations that are biological and pre-specified in our genes.” It is not at all clear, for example, how psychological adaptations map onto genes.

Homunculus fallacy:

Involves an explanation of a psychological construct or process that is ultimately based on a regressive assumption that must invoke a “middle-man” or “man-in-the-head” to explain itself.

Bob: “The mind processes information according to certain rules or algorithms.”
Jan: “What part of the mind oversees the processing or manipulation of data?”
Bob: “another part of the system…”
Jan: “what part of the system processes or manipulates that part of the system?”
Bob: “another part…” (There is an infinite regress, where one solution to the regress seems to imply that there is ‘a little man in our heads’ that does the manipulation of cognition.”

These are but a small selection of logical fallacies that can prevent us from doing good science. Know them, and you will be better prepared to catch the poor reasoning of others (and of your own).

Comments are closed.