If you want the verb to be in the infinitive, then you're going to need another verb in the sentence as well. That is because an infinitive in a sentence, although it is a form of the verb, is usually being used in the place of another part of speech like a noun, adjective, or adverb. Words that are formed from verbs but that are not used like verbs are called 'verbals' in English grammar. I'll give you an example. Take a look at the following sentence which uses the infinitive 'to play': Kittens love to play, Now compare that to this sentence (which doesn't use an infinitive): Kittens love milk. In the second sentence, you can easily see that the subject is the noun 'kittens', the verb is 'love', and the object is the noun 'milk'. Now compare that to the first sentence and you'll see that the basic structure of the two sentences is identical; the only difference is that the noun 'milk' has been replaced with the infinitive 'to play'. In this sentence, 'to play' has become a verbal taking the place of a noun in the other sentence. Since it's not acting like a verb you need another (conjugated) verb ('love') to make a sentence. Verbals can take the place of adjectives and adverbs as well: The doctor to call is Dr Jones. ('to call' is acting like an adjective). I can't wait to hear. ('to hear' is acting like an adverb). Note that in these cases there is still another verb in each sentence ('is' and 'wait' respectively). As a final example, let's take a sentence from one of the comments on your question above: This device governs the rotation speed of the drive shaft. This sentence does not use an infinitive. You would only use 'the infinitive ('to govern') as a verbal and then of course you'd need another (conjugated) verb. Here's an example where 'has been designed' is the conjugated verb and 'to govern' is the infinitive used as a verbal. This device has been designed to govern the rotation speed of the drive shaft. Hope this helps.

George Schneider! Much obliged!

米凯文 Calvin Miller! Thank you so much for your help!

In regard to an engine: This device governs the rotation speed of the drive shaft.

The citizens expect the government to govern. My paycheck will govern what I spend. We should allow reason to govern this discussion. I'm not an expert in grammar but I hope this helps.