+434.+ Remember that a simple sentence is one that contains a single
statement, question or command. It is a clause, for it contains a
subject and a predicate; but it contains only the one subject and the
one predicate. A sentence containing two principal clauses, or a
principal clause and a subordinate clause, would contain two complete
statements, questions or commands, therefore it would not be a simple
sentence, but compound or complex.
Remember, however, that the simple sentences may contain two or more
subjects with the same predicate, or two or more predicates with the
same subject, or both a compound subject and a compound predicate.
+435.+ The modifiers in a simple sentence are always words or phrases.
The modifiers of the subject are either adjectives or adjective phrases.
The modifiers of the predicate are either adverbs or adverb phrases. If
an adjective or an adverb clause is used as a modifier, then the
sentence is no longer a simple sentence, but becomes a _complex_
sentence, for it now contains a dependent clause.