The five basic sentence forms (or "structures") in English are the declarative, interrogative, exclamative, imperative and the optative.
While communication is traditionally defined as the transfer of information, the two terms, under present context, are differentiated as follows below: These types of sentences are more intended for the speaker's sake than for any potential listener.
(Speculated because scientists will never truly be able to understand non-human forms of communication like we do our own; although studies with "talking" primates have clued us in to a certain degree.)
An optative sentence describes wishes, desires, blessings, curses, prayers or hope regarding a given action.
It is related to the subjunctive mood, a grammatical feature that indicates the speaker’s attitude toward something, such as a wish, emotions, judgment, possibility, opinion, obligation, or action that has yet to occur.
Informative sentences are more for the mutual benefit of both the listener and the speaker, and, in fact, require more of an interaction between both parties involved.
They are more intentional or premeditated, less essential, more cooperative, and they aim to either provide or retrieve information, making them quintessential abstractions.
But perhaps the most differentiating quality that distinguishes informative sentences from the communicative is that the former more naturally and freely make use of displacement.
Displacement refers to information lost in time and space which allows us to communicate ideas relating to the past or future (not just the now), and that have taken or can take place at a separate location (from here).
In its most basic sense, a declarative states an idea (either objectively or subjectively on the part of the speaker; and may be either true or false) for the sheer purpose of transferring information.
Its effort is to try to gather information that is presently unknown to the interrogator, or to seek validation for a preconceived notion held.