A conclusive presumption (also known as an irrebuttable presumption) in English law is an presumption of law that cannot rebutted by evidence and must be taken to be the case whatever the evidence to the contrary.

For example, the doli incapax rule conclusively presumes that a child less than ten years old cannot be held legally responsible for its actions, and so cannot be convicted for committing a criminal offence. The age was seven at common law, and raised by the Children and Young Persons Act 1933 to eight and by the Children and Young Persons Act 1963 to ten. A similar rebuttable presumption, that a child between the ages of ten and fourteen was not capable of committing a criminal offence, was abolished by the Crime and Disorder Act 1998.

Many conclusive presumptions have been abolished in recent years. For example:

• the rule that conclusively presumed that a boy under the age of 14 years cannot have sexual intercourse, and so cannot therefore be convicted as a principal for the offences of rape, buggery or any other offence where the actus reus involves sexual intercourse (abolished by the Sexual Offences Act 1993)
• the year and a day rule, which conclusively presumed that a death was not murder (or any other form of homicide) if it occurred more than a year and a day since the act (or omission) that was alleged to have been its cause (abolished by a Law Reform (Year and a Day Rule) Act 1996).
• the rule that, by marriage, a wife was conclusively presumed to have given her irrevocable consent to sexual intercourse with her husband, so a husband could not rape his wife (the offence of rape was then defined in section 1 of the Sexual Offences Act 1956 as "unlawful" sexual intercouse without consent, and the word "unlawful" was taken to make a distinction from "lawful" sexual intercourse within marriage). This rule was overturned by the House of Lords in the case of R. v. R. in 1991, and its abolition made clear by the Criminal Justice and Public Order Act 1994, which deleted the word "unlawful" from the definition.

See also

• Rebuttable presumption
• Presumption of fact

English law