"to" as in "To err is human." It turns a verb into a noun or adverb. It works similar to a gerund, which is formed by adding -ing, as in "Erring is human." A split infinitive occurs when there are words between "to" and its verb, for example "to boldly go where no man has ever gone before."
infinitive: be past: was/were past participle: been
infinitive: choose past: chose past participle: chosen
infinitive: think past: thought past participle: thought
infinitive: sit past: sat past participle: sat
So is not an infinitive. An infinitive is [to + a verb].
A bare infinitive is a linguistic term for the infinitive form of a verb, without the particle "to".
A zu-infinitive is a German infinitive form created by adding or infixing the particle zu and used in subordinate clauses.
A zu-infinitive is a German infinitive form created by adding or infixing the particle zu and used in subordinate clauses.
infinitive: mean past: meant past participle: meant
infinitive: arise past: arose past participle: arisen
infinitive: become past: became past participle: become
infinitive: drink past: drank past participle: drunk
infinitive: be past: was/were past participle: been
infinitive: think past: thought past participle: thought
infinitive: choose past: chose past participle: chosen
infinitive: sit past: sat past participle: sat
you are derives from the infinitive of to be. The infinitive that belongs to 'you are' is 'to be'.