These are the most easily confused modifiers. Very often, a modifier comes after a simple verb, but is not a verb! The only time a participle can be a verb (an action) is when it is in the compound tense of the present or past perfect.
In first three examples, the participle is describing a noun: “a finished assignment," “a rewritten assignment," and “a considered Mr. Smith." Compare these examples with the three below in which the participle acts as a verb. Notice that the perfect tense must be used in each case.
He is finished with the assignment.
The assignment will be rewritten tomorrow.
Mr. Smith was considered for the job.
He has finished with the assignment.
He had rewritten the assignment.
Mr. Smith has considered the job.