Acts done by several persons in furtherance of common intention (Section 34):

“When a criminal act is done by several persons in furtherance of the common intention of all, each of such persons is liable for that act in the same manner as if it were done by him alone.”

Common intention is a concept of English law which is first decided in the case of R v. Cruse 1838. The gist of this definition is that there is a joint liability, in the doing of the criminal offence. This liability is based on the existence of a "common intention''.
For this, there must be prior consent or prearranged plan. There must be a prior meeting of minds. For Instance, Several persons may attack ‘A’ each with an intention to kill A, but this is not common intention as there is no "meeting of minds". In such a case each is liable for whatever injury he has caused. The leading case is Krishna Govind Vs. State of Maharastra. This section is only a rule of evidence, and does not create any offence.
When offence is committed by several person acting in collaboration all such person as known as joint offender. Section 34 and Section 149 deal with Joint liability. Section 34 is only a rule of evidence and does not create a substantive offence.

Ingredient of Section 34:

Criminal Act- criminal act used in Sec 34 does not refer to individual act where a crime is committed by group of persons.

Criminal Act is done by several person- Several person means two or more than two persons, criminal act must be done by several person.

Criminal Act done by such persons in furtherance of common intention of all of them- the expression “in furtherance of common intention of all” did not exist in the original code, but was added by the Amending Act of 1870 after the case of Ganesh Singh v. Ram Raja (1869) SC.

Over act must be done by any person- participation of person in some manner in the act constituting the offence by person sought to be prosecuted

Barendra Kumar Ghose v. emperor 1925 (PC)

In this case, Privy Council laid down even if appellant did nothing as he stood outside the door, it is to be remembered that in crimes as in other things, they also serve who only stand and wait.

Mahboob Shah v. Emperor 1945 PC

In this case, Privy Council laid down that common intention within the meaning of Section 34 implies a pre-arranged plan and to convict the accused of an offence applying the Section it should be proved that criminal act was done in concert pursuant to the pre-arranged plan.

Constructive liability in criminal law means liability of person for an offence which he has not actually committed. Sec 149 of Indian Penal Code, 1860 deal with constructive liability.

Every member of unlawful assembly guilty of offence committed in prosecution of common object (Sec 149) —

“If an offence is committed by any member of an unlawful assembly in prosecution of the common object of that assembly, or such as the members of that assembly knew to be likely to be committed in prosecution of that object, every person who, at the time of the committing of that offence, is a member of the same assembly, is guilty of that offence.”

Common object is different from common intention. It does not require a prior concert and a common meeting of minds before attack

K C Mathew v. State of Travancore Cochin AIR 1956 SC

people gathered at deed of night armed with crackers, choppers and sticks to reuse persons who were guarded by armed police. It was held that they must have known that murder will be committed and a conviction for murder – cum-rioting was justified.

Section 34 read with Section 302  

In Banu Singh V. Emperor, it was held that there must be a pre-arranged plan and meeting of minds to convict the accused. In this case, Mala Singh had given one blow to the deceased Dala Singh, but Banu was responsible for killing.

There was no plan or meeting of minds to make them both liable for murder. It was held that Mala Singh was liable for causing grievous hurt.

In Ishwari V. State, two brothers A and B had attacked D and killed him at the dead hour of the night at D's residence. A had attacked with a sharp weapon, and B had attacked with lathi. Held there was common intention.

Difference between Common Intention and Common Object-

1. Under Section 34 number of persons must be more than one. Under Section 149 number of persons must be five or more.

2. Section 34 does not create any specific offence but only states a rule of evidence. Section 149 creates a specific offence.

3. Common intention required under Section 34 may be of any type. Common object under Section 149 must be one of the objects mentioned in Section 141.

4. Common intention under Section 34 requires prior meeting of minds or pre-arranged plan, i.e. all the accused persons must meet together before the actual attack participated by all takes place. Under Section 149, prior meeting of minds is not necessary. Mere membership of an unlawful assembly at the time of commission of the offence is sufficient.

5. Under Section 34 some active participation is necessary, especially in a crime involving physical violence. Section 149 does not require active participation and the liability arises by reason of mere membership of the unlawful assembly with a common object.