Consider the following sentence:
(1) He is at the station.
We could ask
(2) Where is he?
and we may also ask:
(3) He is at what?
(4) What is he at?
However (3) and (4) are marked in the linguistic sense. (2) seems the more natural question form. Consider (5):
(5) He is there.
We are no longer able to ask (3) or (4). This shows that at the station in (1) is equivalent to there in (5). It is a constituent, an adverbial to be exact, and in (1) a prepositional phrase more precisely.
In any English sentence there are either zero, one, two or three actants.
Actants are the “participants” of the sentence. They are either people or things. In (1) below the action of “to rain” itself is the “zero” actant.
(1) It is raining.
“It” is the dummy subject.
In (2) and (3) the subjects “Peter” and “Charlene” are the actants respectively.
(2) Peter is swimming.
(3) Charlene is a teacher.
In (2) the act itself is performed by the subject “he”. In (3) “Charlene” and “the teacher” are one and the same person. Only one actant is involved in the description of the situation. In (4) and (5) below there are two actants. In (4) they are “Dave” and “the ball”. In (5) they are “the people” and “Hilary”. Since “Hilary” and “he president” are one and the same person we do not count the president as an actant.
(4) Dave kicked the ball.
(5) The people made Hilary the president.
In (6) we have three actants.
(6) Tony gave Leslie a presnet.
They are “Tony”, “Leslie” and “a present”.
Technically, it is possible to have more actants (and more than likely some languages do) but in English our limit seems to be three. More complex sentences will be simple sentences in disguise.
Consider this sentence:
(1) He put the bag down.
The parts of the sentence are He (S) / put (V) / the bag (O) / down (A). The removal of A (adverbial) would render the sentence incomplete. In other words, the A is obligatory.
Some teachers call this sentence SVO but that would make “the bag down” the object of the sentence, which of course is not true. It is true the V and A make a set. We can see this by rearranging the syntax elements to
(2) He put down the bag.
By doing so we can explain it as SVO where put down is the single unit of V. A problem arises when the A is a longer element, and cannot be moved easily like (2). For example,
(3) He put the bag on the overhead baggage shelf.
is a perfectly good sentence and again it is SVOA. But if we try to rearrange it as in (3a)
(3a) He put on the overhead baggage shelf the bag.
we find the sentence to be clumsy and unnatural.
For this reason it is better to teach SVOA rather than try to slim the sentence patterns to less for the sake of brevity. Sometimes this can be too much to be useful.
Over the years of teaching and writing I have noticed how much more emphasis had been given to words (morphology) over sentences (syntax). Perhaps it is because sentences are mistakenly thought of as so much harder to pin down. When people see a sentence of twenty words they think of twenty things. Rarely do they think of the sentence as one thing. In my opinion, a sentence is a unit of complete communication. It is not the only unit to be considered complete. Words, of course, are considered (and taught as) complete units. Fair enough. We can use words out of sentence-context and still get some kind of meaning across, but just not very well. But because of the inaccuracy, it seems logical to work with the unit which best gives a “complete” meaning, instead of working with units which do not make a unit of communication. It is for this reason that I believe that syntax should be given priority in teaching and learning.
I have talked about the seven sentence patterns here. Those are all simple sentences. A simple sentence contains a single verb, that is, one clause. Complex sentences contain more than one verb, or two or more clauses.
An SVO sentence theoretically can have three clauses, having one each for the subject, verb and object. It is possible to have more clauses (and/or phrases) by adding optional elements like adjectives and adverbs. But the more clauses you add the more complex and difficult it becomes to understand what-is-what within a sentence.
It is advisable not to make add too many clauses to a sentence. If you do find you have created a long and difficult to understand sentence on your hands break it down to two or more shorter simpler sentences.