In act 2.1 of the tragedy of julius caesar, why do the conspirators not swear an oath?

they intend to take an oath but forget to do so.
brutus thinks they are dishonest men and knows an oath will not mean anything to them.
in ancient rome, the law stated that they could only take an oath if their fathers were present.
brutus thinks that honest men will follow through on their intentions; therefore, they do not need to swear an oath.