A method of mathematical argumentation that begins by assuming the negation of the statement to be proven is true. Subsequent logical steps are then applied, aiming to derive a contradiction. This contradiction, typically arising from established axioms, theorems, or given information, demonstrates that the initial assumption of the statement’s negation must be false, therefore validating the original statement. In the realm of spatial reasoning, for instance, establishing that two lines are parallel might involve initially supposing they intersect. If that supposition logically leads to a contradiction of previously established geometric principles, the original assertion that the lines are parallel is affirmed.
This method offers a powerful approach when direct demonstration proves elusive. Its strength lies in its ability to leverage known truths to disprove a contrary assumption, thereby indirectly validating the intended claim. Historically, it has been invaluable in establishing cornerstones of mathematics, and has broadened the scope of what can be formally proven. By providing an alternative means of validation, it expands the arsenal of tools available to mathematicians, allowing them to tackle problems that would otherwise remain intractable.