I think this would apply in this example...
verbal auxiliary
1 -- used with the past participle to form the present perfect, past perfect, or future perfect <has gone home> <had already eaten> <will have finished dinner by then>
2 : to be compelled, obliged, or required -- used with an infinitive with to or to alone <we had to go> <do what you have to> <it has to be said>
- had better or had best : would be wise to
Chris
http://www.hearseesay.com