
stackexchange.com
https://ell.stackexchange.com/questions/219533/whe…
infinitives - When we should add "to" before verb? - English Language ...
Generally, the question of whether to use the infinitive with "to" or the infinitive without "to" depends on the particular word (verb, adjective, noun) which commands the phrase, and you just have to learn that. For example, modals, such as should, must, take an infinitive without "to", while verbs like ought, have (to) require the "to", even though they mean pretty much the same: I should go ...