A tautology is a logical statement which, by its very structure, must be true. For example:
- A ∨ ¬A (A or not A)
In this example, A represents a statement, such as "God exists", "my shirt is white", or "all rabbits are green". But no matter what value we assign to A, the statement above is true:
- Either God exists, or God does not exist.
- Either my shirt is white, or my shirt is not white.
- Either all rabbits are green, or else it is not the case that all rabbits are green.
"Natural selection is a tautology"
Creationists often argue that natural selection is a tautology:
- "Natural selection" is defined as "survival of the fittest".
- Those individuals in a population who survive are defined to be the fittest.
- Therefore, "survival of the fittest" means "survival of those who survive" or "those who survive, survive".
"Those who survive, survive" is a tautology because there is no condition under which it could possibly be false.