Just lifted this one (copied and pasted) from RomLaw (a study aid). Haven't read this thread over recently to see if there's a similar one. Haven't read the mnemonic over to check if it's accurate either, but it looks good at first glance:
Four requirements must be met to reduce a killing from murder to manslaughter:
C. Causal connection (S.ubjective): There must be a causal connection between all three requirements infra. It is murder to kill an innocent bystander, but if this is done by accident in missing the initial provoker or is done by reasonable mistake, it is manslaughter.
A. Adequate provocation (O.bjective): There must be adequate provocation. To be recognized by law as adequate, it must deprive a reasonable person of self-control for the moment.
S. Sudden heat of passion (O.bjective): The killing must have been in the sudden heat of passion and must have occurred before there was a reasonable opportunity for the passion to cool. The majority determines this by the use of a reasonable person standard of a reasonable person suffering from similar afflictions. The minority ignores all afflictions.
H. Heat of passion (S.ubjective): The killing must have been in the heat of passion. The killing must have followed the provocation before the defendant had an opportunity to cool off. The defendant must have killed while his actions were directed by passion rather than by reason.