Most sentences can be classified as either loose (or cumulative) or periodic.
The loose (or cumulative) sentence is our common means of expression. We begin with a subject, followed by an action (the verb), and then additional details.
"Sam, our class president, hopes to attend Harvard University this fall."
The loose (or cumulative) sentence presents the subject and verb near the beginning, such that the reader knows who or what is being discussed and what is happening.
The periodic sentence is a suspended sentence; in other words, the reader either does not know who or what is being discussed and/or what is happening until the final word of the sentence. Well-crafted periodic sentence hold the reader in suspense. The reader anticipates something important, but writer holds it back, building tension, until the final moment of revelation. In the following examples, the actual completed sentence is underlined. Note how the writers begin with a series of phrases or clauses, establishing the scene or situation prior to the main statement:
While he was declaring the ardour of his passion in such terms, as but too often make vehemence pass for sincerity, Adeline, to whom this declaration, if honourable, was distressing, and if dishonourable, was shocking, interrupted him and thanked him for the offer of a distinction, which, with a modest, but determined air, she said she must refuse. (Ann Radcliffe, Romance of the Forest)