Rule: If the subject of the infinitive clause object is not co-referential with the subject of the main verb, it must be expressed. If the two subjects are co-referential, the subject of the infinitive is usually omitted but must be expressed following certain (main) verbs.
Examples of errors:
In German it is frequently possible to omit the subject of an infinitive clause object where it is not possible in English:
Er sagte, sie hereinkommen zu lassen.
*I told to let her come in.
I told John to let her come it.
In English, if the subject of the infinitive is different from (i.e. not co-referential with) the subject of the main verb, as in the example above, and as in (l)-(2), the infinitive subject (one) cannot be omitted. The one exception to this rule is say in the sense of 'order', e.g.:
She said (for us) to be home by midnight.
If the infinitive subject is co-referential with the main subject, as in (3)-(5), the rule is more complicated. In this case, the co-referential infinitive subject must be omitted with most (main) verbs, e.g.:
He
wants
expects
hopes
desire
likes
to go swimming
*himself to go swimming
But there are a number of verbs that are followed by be as infinitive and require the infinitive subject to be expressed (as a reflexive pronoun), even though it is co-referential with the main subject. These verbs include think (cf. (3)), fancy (cf. (4)), feel (cf. (5)), acknowledge, allow, appoint, assume, believe, cause, choose. claim. elect. find. forbid, expect, get, hold, imagine, know, proclaim, suppose, compel, encourage, force. help, induce, persuade, permit, teach, tell, etc. With some of these verbs, not the subject of the infinitive, but the infinitive itself, may be omitted, e.g.:
I think myself (to be) able to make a speech.