Where two or more persons together form a common intention to commit a particular criminal act, and that act is actually done by one or more of them in furtherance of this shared intention, each person forming part of the common intention is held liable for the act exactly as if that person had personally done it alone, regardless of who among the group actually performed the physical act itself. The doctrine of common intention thus fixes joint liability on every participant sharing the same prior meeting of minds, not merely on whoever happened to strike the final blow or otherwise directly execute the criminal act.

For the doctrine to apply, several elements must be established. First, there must be a genuine, shared common intention formed before the criminal act is carried out -- a real meeting of minds regarding the specific criminal act to be done, rather than a mere presence at the scene or a general awareness that some vague wrongdoing might occur. This common intention may be formed on the spur of the moment, immediately before the act, and need not have been planned long in advance, provided a genuine, shared intention to commit the specific act did, in fact, exist at the relevant time. Second, the act actually done must be in furtherance of this shared common intention, meaning the act must be one that flows from and advances the agreed common purpose, rather than being an unconnected, independent act by one participant that goes beyond what was actually intended by the group.

A person's mere presence at the scene of a crime, without sharing in the actual common intention to commit that specific criminal act, does not by itself make that person liable under this doctrine; presence alone, without a genuine, shared intention regarding the specific act committed, falls short of what the doctrine requires. Similarly, where one member of a group, acting entirely on their own initiative and outside what the group had actually, genuinely intended, commits an act that goes beyond the shared common intention -- an independent act unconnected to the agreed common purpose -- the other members who did not share in this particular, additional intention are generally not liable for that specific, additional act, even though they may remain liable for whatever act was actually within their own genuine, shared common intention.

The doctrine of common intention, properly understood, distinguishes between the liability that arises when a group genuinely intends a particular criminal outcome together, however that shared intention is eventually carried out by any one of them, and the very different situation where a person merely happens to be present while another commits an act the first person never actually shared any genuine intention to bring about.