A conclusive presumption (in Latin, praesumptio iuris et de iure), also known as an irrebuttable presumption, is a type of presumption used in several legal systems.
In English law, a conclusive presumption is a presumption of law that cannot be rebutted by evidence and must be taken to be the case whatever the evidence to the contrary.
For example, a child below the age of criminal responsibility cannot be held legally responsible for his or her actions, and so cannot be convicted of committing a criminal offence. The age has continually been under debate with adjustments being made in line with rulings, the results of psychological research and to some extent public pressure. The age was seven at common law, and raised by the Children and Young Persons Act 1933 to eight (section 50) and by the Children and Young Persons Act 1963 to ten, at which it remains.
In Australian law, it is a conclusive presumption that no child under the age of 10 can be held responsible for criminal action. This presumption exists to protect children by acknowledging that they do not have sufficient development to understand the gravity and consequences of committing a criminal act.