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Garbage in garbage out

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Cogito ergo sum
Logic and rhetoric
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General logic
Bad logic
On two occasions I have been asked, "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" … I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.
Charles Babbage,Wikipedia inventory of the mechanical computer[1]

Garbage in, garbage out (GIGO) is a long-standing principle of computer programming and algorithm design. It means that it doesn't matter how good your logic is; if your input is bad, your output will be nonsense. In philosophical terms, your argument may be valid, but not sound.

Let's examine Pascal's wager as an example of how this applies to debate tactics:

  1. If you believe in God and God does exist, you will be rewarded with eternal life in Heaven: thus an infinite gain.
  2. If you do not believe in God and God does exist, you will be condemned to remain in Hell forever: thus an infinite loss.
  3. If you believe in God and God does not exist, you will not be rewarded: thus a finite loss.
  4. If you do not believe in God and God does not exist, you will not be rewarded, but you have lived your own life: thus a finite gain.

A purely logical analysis of the statements as such suggests that the best option must necessarily be to believe in God. However, it can easily be argued that Pascal's premises were wrong. Pascal assumes that only one kind of faith (and therefore, one God) mattered. Pascal ignores the variety of human religious experiences, immediately invalidating the premises themselves, and therefore making the logical conclusion, garbage.

Common sources of garbage input include cherry-picked or elided data, disproved "common sense", small sample sizes (and anecdotes), and outright lies, as well as equivocation over definitions. Garbage outputs are occasionally correct, but if they got there by the wrong path, they aren't of very much use.

See also[edit]


  1. Passages from the Life of a Philosopher by Charles Babbage (1864) Longman, Green, Longman, Roberts & Green.