R v Instan (1893) 1 QB 450 is an English criminal law manslaughter case confirming how the actus reus of manslaughter can be one of inactive negligence (that is, neglect), as the common law imposes a basic duty of care onto an adult who voluntarily undertakes the regular care of another.

The case's jurisprudential explanations for how the common law is arrived at by such a research and analysis process, not in a vacuum but rather by reference to strong moral obligations.

The adult niece was found guilty of manslaughter on the basis that she had accepted her aunt's money in to pay for their food.

Lord Coleridge CJ wrote that despite the lack of statute or precedent, it would be "a slur on justice" were the niece's behaviour to go unpunished: We are all of opinion that this conviction must be affirmed.

it is unnecessary to say more than that upon the evidence this conviction was most properly arrived at.The niece would be disinherited by law by virtue of the forfeiture rule.