... subject of the sentence is the agent, the person who has to the job, then we use the active infinitive, not the passive If the subject of the sentence is not the agent, then we use the passive infinitive ... passive infinitive - These windows have to be painted - The homework was to be done by the next day - After the subject there, we can use either an active or a passive infinitive - There are a lot ... machine isn't safe to use - The piano is too heavy to move - That box isn't strong enough to sit on If we use a phrase with by and the agent, then the infinitive is passive - The piano is too heavy...