TO-infinitive

To 如果是做 infinitive, 後面的 verb 是用 base form of verb, without special ending.
The base form of the verb is the simplest form of the verb ~ the one listed in a dictionary.

例子:
He wants to go. (不是 goes, going, went or gone)
She decided to apply for the job. (不是 applies, applying or applied)

但是 to 除了做 infinitive 之外, 還可以做 preposition, 後面的 verb, 變了用 verb-ing, (gerund.)
只有 verb-ing 作 noun 時, 才是 gerund.

例子:
I am looking forward to seeing you. (to 是 preposition, seeing 是 gerund)
He is accustomed to driving at night.
The Green Party is dedicated to protecting the environment.
We may have to resort to using untrained staff.

問題要清楚知道 to 在句子中是做 infinitive 或 preposition.
前置詞 (preposition) 後面可用 noun, noun phrase, gerund 代替.
He is accustomed to the dark.

小心:
She used to drive in London. (to 是 infinitive)
She is used to driving in London. (to 是 preposition)
這兩句子意思不同

題外:
因為 to 可以做前置詞, 有時後面 verb form 變了用 past participle 作 adjective.
“A sermon to unconverted sinners” ~ Title
(unconverted 是 past participle, used as an adjective)

TO 後面是不是永遠都不變??
ANSWER:是