There is considerable overlap between the four words, and it is quite possible for D to participate in more than one way.
‘Aiding’ As indicated above, this means to provide some assistance before or during the commission of a crime by the principal. The scope of aiding is demonstrated by the case of Robinson  UKPC 3, in which D was convicted of aiding a murder committed by E by acting as a lookout/backup. E had killed two men (who were twin brothers) with a baseball bat, while D guarded the door to the room where the attack took place. The brothers’ decomposing bodies were found a month later down a cliff. D appealed, unsuccessfully, to the Privy Council. The Court stated that aiding ‘imports a positive act of assistance’ but added that:
‘Of course, that positive act of assistance may sometimes be constituted by D2 being present, and communicating to D1 not merely that he concurs in what D1 is doing, but that he is ready and willing to help in any way required. The commission of most criminal offences, and certainly most offences of violence, may be assisted by the forbidding presence of another as back-up and support.’