For example, needs to account for why if the sentence P and Q is true, then so is the sentence Q and in order to do that it assigns a certain structure, for example as on the handout in my assigned structure and brackets P Q.  Erm   anyway erm it just has and has a separate particle operating on two distinct sentences that are not ordered  syntax needs to account for the well-formedness of the structure, sorry  P and Q. The ill-formedness of P Q and  the similar grouping of and with or that is in English  between sentences and where you can find one and find another  but not with, not  you don't say John loves Mary not Peter loves Jill.