What is a logical fallacy?

Question
Someone accused me of making a logical fallacy. What is a logical fallacy? What is equivocation?
Answer
Logic is the study of reasoning — the nature of good and proper reasoning and of bad and improper reasoning. A logical fallacy, then, is an invalid form of argument — incorrect or faulty reasoning.

What is equivocation? This is a logical fallacy that stems from the ambiguous meaning of certain terms/words. An illustration may help:

  • Only man is logical.
  • No woman is a man.
  • Therefore, no woman is logical.

The word "man" in the first statement above literally means all mankind. In the second statement, man means only a man, but not a woman; for instance, Adam, but not Eve. Therefore, because of the subtle shift in meaning of terms/words, this makes the conclusion in the third statement improper, incorrect, and literally false.

There are numerous types of logical fallacies. Here are a few: (1) affirming the consequent; (2) anthrocentric fallacy; (3) appeal to authority; (4) a priori fallacies; (5) arguing from "is" to "ought"; (6) argumentum ad baculinum; (7) argumentum ad captandum; (8) argumentum ad crumenam; (9) argumentum ad hominem; (10) argumentum ad ignorantiam; (11) argumentum ad lazarum; (12) argumentum ad misericordiam; (13) argumentum ad populum; (14) argumentum ad verecundiam; (15) argumentum ex silentio; (16) begging the question; (17) circular reasoning; (18) equivocation; (19) fallacy of false alternatives; (20) fallacies of interrogation; (21) flamboyance; (22) gadarene swine fallacy; (23) genetic fallacy; (24) hasty generalization; (25) if-then fallacies; (26) ignoratio elenchi; (27) invincible ignorance; (28) naturalistic fallacy; (29) non sequitur; (30) paralogism; (31) performative contradiction; (32) petitio principii; (33) poisoning the wells; (34) post hoc ergo propter hoc; (35) red herring; (36) straw man fallacy; (37) tu quoque fallacy; and (38) undistributed middle, etc.

I'll leave it up to the reader to investigate various definitions of the words and phrases above.

Answer by Dr. Joseph R. Nally, Jr.

Dr. Joseph R. Nally, Jr., D.D., M.Div. is the Theological Editor at Third Millennium Ministries (IIIM).