A genitive absolute links a participle and a noun or pronoun in the genitive case and is only loosely connected to the rest of the sentence. The subject of the sentence is not the subject of this participial construction.
Participle (gen.) + noun/pronoun (gen.)
o[ ga>r ]Ihsou?j e]ce
For Jesus had withdrawn, a crowd being in the place (Jn. 5:13).
Infinitives are verbal nouns usually indicated in English by a “to” + verb (e.g., He went inside to call a friend.). While in English an infinitive does not take a subject, it may take an object or be modified by some qualifier. For example: “He came to put the ball in the box” uses “the ball” as the object and “in the box,” which describes location, to modify the infinitive “to put.” With Greek infinitives, the tense indicates aspect rather than time of action:
Present represents progress/immediacy foregrounding action.
Perfect represents state of affairs frontground/dwelt upon action.
As a noun, an infinitive can be the subject of a sentence or the object of a finite verb. In Greek an infinitive may go with a noun in the accusative that functions as its subject.