The Internalist Justificatory Function of Reductio Ad Absurdum

In the present essay it is discussed the main features of reductio ad absurdum as a source of justification. These properties are consequences of the employment of contradictions as a reason for proving if a statement is true. Although a valid deductive argument can build an internalistic justification, I would suggest that the justification obtained by reductio ad absurdum cannot be externalist. This is because contradictions as reasons can be considered internal states from different definitions.