In this example, there is a noun belief that can be described like acceptance that something is true but there is no evidence, and believing in this without evidence. The noun in the singular is a belief, but in this example, it should be in the plural. The noun with ending in -f get -s in the plural. This noun does not change -f into -v like in examples: knife-knives or wolf- wolfes. If it changes -f into -v it should be believes and that is a present time of the verb to believe.
May is where you say like for instance I may clean my room. I am just saying there is a chance I might do it. and shall is justa saying I absolutly going to do it.
