Con algunas expresiones idiomáticas no se utiliza la preposición to al añadir un infinitivo.

Expresiones con infinitivo sin to
he had better ... le convendría...
he had best ... le convendría...
he had/would rather ... preferiría ...
he would sooner ... preferiría ...
he would (just) as soon ... tanto le gustaría...como
he couldn't (help) but ... no podía de otra manera ...
Ejemplos
He had better go by bus; the weather is too bad to go by bike.
She had best stay at home, she is too ill to go to work.
We had/would rather go to the theatre.
They would sooner sell their house than borrow money.
She would (just) as soon read a good book as go for a walk.
He couldn't (help) but laugh.