A persuasive definition fallacy occurs when a term that should simply refer to a topic under debate is defined by an arguer in a non-neutral way, so as to imply that the arguer's position is the correct one. By so doing, the arguer attempts to settle the debate before it starts, since the key term used to discuss the topic already decides the issue.

Examples are: "abortion is the murder of an unborn child" or "abortion is nothing more than a mother controlling her own body". Each of these is a persuasive definition -- to accept either is to declare one position in the abortion debate the correct one.

A definition that does not commit this fallacy could be: "abortion is the termination of a pregnancy by human intervention."

Other examples would be "an atheist is someone who refuses to acknowledge God" or "a theist is someone who believes in the illusion of a supernatural being".

See also: definist fallacy