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Irrational vs. Illogical: What's the Difference?

Edited by Harlon Moss || By Janet White || Updated on October 3, 2023
"Irrational" refers to behavior or thought patterns that are not based on reason or clear thinking, often driven by emotion or instinct. "Illogical" means not making sense according to established rules of logic or reasoning.

Key Differences

"Irrational" primarily denotes actions, decisions, or thoughts that are not grounded in reason or sensible judgment. This term often involves the influence of emotions, prejudices, or instincts that override rational thinking. "Illogical," on the other hand, describes statements, arguments, or actions that violate the principles of logical reasoning. While both terms imply a departure from rationality, their focus and implications are different.
The term "irrational" is frequently used in the context of human behavior and decision-making. For example, someone acting out of fear or love might be described as irrational if their actions lack objective reason. "Illogical" is more often used to critique the structure or content of an argument or statement, pointing out inconsistencies or contradictions within a logical framework.
From a grammatical standpoint, both "irrational" and "illogical" are adjectives, but they can also function as nouns when referring to the quality of being irrational or illogical. For example, "the irrationality of the crowd" or "the illogic of the situation."
In psychological contexts, "irrational" may refer to behaviors or beliefs that are not in one's best interest, even harmful. In contrast, "illogical" in scientific or philosophical discussions pinpoints flaws in reasoning or argumentation. Essentially, "irrational" is broader and often more subjective, while "illogical" is more specific and objective.
In summary, "irrational" encompasses a broad range of unreasoned behaviors and thoughts, often driven by emotion or instinct. "Illogical" is narrower, focusing on errors in reasoning or logic. Both terms can be used in various contexts but they target different aspects of irrationality.

Comparison Chart

Grammatical Role

Adjective, can also be a noun
Adjective, can also be a noun


Human behavior, psychology
Arguments, philosophy


Emotion, instinct
Logical consistency


More subjective
More objective

Range of Application

Broader in usage
More specific, usually tied to logical principles

Irrational and Illogical Definitions


Not in accordance with mathematics or logic.
The square root of -1 is considered irrational.


Lacking sense or clear reasoning.
The plot of the movie was illogical.


Contrary to one's best interests.
Quitting your job without a plan is irrational.


Inconsistent with facts or reality.
Her illogical statement confused everyone.


Influenced by emotion or instinct.
She made an irrational decision in the heat of the moment.


Contrary to the principles of logic.
His argument was completely illogical.


Lacking sound judgment.
His irrational behavior worried his family.


Violating the rules of valid inference.
The fallacy in his speech was illogical.


Not endowed with reason.


Unsound in argumentation or deduction.
His illogical reasoning led him to the wrong conclusion.


Affected by loss of usual or normal mental clarity; incoherent, as from shock.


Contradicting or disregarding the principles of logic.


Marked by a lack of accord with reason or sound judgment
An irrational dislike.


Without logic; senseless.


Being a syllable in Greek and Latin prosody whose length does not fit the metric pattern.


Contrary to logic; lacking sense or sound reasoning.
I received an illogical reply and that left me standing there feeling confused.


Being a metric foot containing such a syllable.


Ignorant or negligent of the rules of logic or correct reasoning; as, an illogical disputant; contrary of the rules of logic or sound reasoning; as, an illogical inference.


(Mathematics) Of or relating to an irrational number.


Lacking in correct logical relation


An irrational number.


Lacking orderly continuity;
A confused set of instructions
A confused dream about the end of the world
Disconnected fragments of a story
Scattered thoughts


Not rational; unfounded or nonsensical.
An irrational decision


Of a real number, that cannot be written as the ratio of two integers.
The number π is irrational.


A real number that can not be expressed as the quotient of two integers, an irrational number.


Not rational; void of reason or understanding; as, brutes are irrational animals.


Not according to reason; having no rational basis; clearly contrary to reason; easily disproved by reasoning; absurd; - of assertions and beliefs.
It seemed utterly irrational any longer to maintain it.


Not capable of being exactly expressed by an integral number, nor by a ratio of integral numbers; surd; - said especially of roots. See Surd.


Not consistent with or using reason;
Irrational fears
Irrational animals


Real but not expressible as the quotient of two integers;
Irrational numbers


Not based on clear thinking or reason.
His fear of spiders is irrational.


Is "illogical" the same as false?

No, "illogical" means it doesn't follow logical reasoning, but the conclusion may still be true.

What does "illogical" mean?

"Illogical" means not making sense according to rules of logic or reasoning.

Is "irrational" always emotional?

No, "irrational" can be driven by emotions, instincts, or simply lack of reasoning.

Can "illogical" be a noun?

Yes, the noun form is "illogic" or "illogicality."

Is "illogical" always wrong?

No, an "illogical" argument may arrive at a correct conclusion, but through faulty reasoning.

Can arguments be "illogical"?

Yes, "illogical" is often used to describe flawed reasoning in arguments.

Can "irrational" apply to numbers?

Yes, in mathematics, "irrational" refers to numbers that cannot be expressed as a simple fraction.

What does "irrational" mean?

"Irrational" refers to behavior or thoughts not based on reason or clear thinking.

Can "irrational" be a noun?

Yes, the noun form is "irrationality."

Is "irrational" subjective?

"Irrational" is often more subjective and open to interpretation.

Can "irrational" be temporary?

Yes, people can act irrationally under stress but revert to rational behavior later.

Is "illogical" objective?

"Illogical" tends to be more objective, based on established logical principles.

Is "irrational" only for humans?

No, but it is most commonly used to describe human behavior or thoughts.

Can "irrational" actions be justified?

Sometimes "irrational" actions may have underlying reasons that make them understandable, if not justified.

Is "illogical" used in philosophy?

Yes, "illogical" is frequently used in philosophical discussions to identify reasoning errors.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.

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