35. “to do” versus “to doing”



Verbs after “to” are not always in the infinitive form; sometimes they need “-ing” instead



Why is it right to say I look forward to visiting you and not I look forward to visit you? After all, English does not say *I want to visiting you. The answer is that look forward to and want to have different kinds of “to”, which require different things after them.

The “to” after look forward is a preposition, while the other is the to of infinitive verbs (e.g. TO BE, TO HAVE, TO LIKE, and TO INTRODUCE). It is normal in English for verbs after a preposition to have -ing (cf 70. Gerunds) and for infinitive verbs not to have it. These two different uses of to make it the same kind of problem word that is discussed in the post 3. Multi-Use Words.



How do we know that the to of look forward to is a preposition? A useful way to see if any word is a preposition is to check whether it sounds right directly before the + NOUN (see 84. Seven Things to Know about Prepositions). For example, on, off and near are prepositions because it sounds right to say on the bus, off the bus and near the bus. The “to” of look forward to can definitely be used in this preposition way, as shown in the following example, where the verb visiting has been changed into the noun the visit.

(a) I look forward to the visit. 

The “to” of want, on the other hand, is not a preposition, since it does not sound correct with the and a noun directly after it: 

(b) *I want to the visit.

Behaviour before nouns is not the only way to distinguish the two kinds of to. They also divide sentences in different places: 

(c) I look forward to / visiting you.

(d) I want / to visit you. 

In (c) the to is part of the first verb, while in (d) it belongs to the second. We can prove this by considering what to write when there is no second verb, like this: 

(e) I ……………….. the visit. 

If we put look forward into the blank space here, we also need to; but if we put want, using to is not possible. Thus, to is always needed when look forward is used so must be part of it, but it is not always needed when want is used, so it cannot be part of want.



The verb LOOK FORWARD TO belongs to the class of “prepositional” verbs like LOOK AT, DEPEND ON, THINK OF, COPE WITH and PUT UP WITH: all end with a preposition so that they all need either a noun or -ing after them (see 44. Troublesome Prepositional Verbs).

The presence of the adverb FORWARD might be one reason why we do not naturally think of LOOK FORWARD TO as a prepositional verb, since it suggests the verb is “phrasal” instead (see 139. Phrasal Verbs). Another reason might be the rarity of to in prepositional verbs. Another might be the tendency of near-synonyms of LOOK FORWARD TO, like WANT, EXPECT and PLAN, to have the non-prepositional to after them (see 140. Words with Unexpected Grammar 2, #[c]).

Remembering to put following verbs into the -ing form is not the only problem that LOOK FORWARD TO gives; for another, see 132. Tricky Word Contrasts 4 (point #5).

The preposition to gives similar problems in a few other English verbs of a mostly prepositional nature. One of the most confusing for speakers whose mother tongue is not English is BE USED TO (actually the verb BE followed by the adjective USED and the preposition TO), which expresses the meaning of familiarity and conquered difficulty, as in this example:

(f) Children in nurseries are used to seeing less of their parents.

This says that children in nurseries today do not have much difficulty seeing less of their parents – they have learned to accept it. Used to is a description of how they are now, not what they once did.

Errors with BE USED TO (DO)ING come from the fact that English also has the verbs USED TO (DO), expressing a repeated past practice that has now stopped, and BE USED (TO DO), the passive of the ordinary verb USE (meaning “be employed”) combined with an optional TO showing purpose or function (see 60. Purpose Sentences with “for” and 119. BE before a “to” Verb). Compare:

(g) Children used to see less of their parents than they do now.

(h) Children in nurseries are used (in order) to train teachers.

The first of these is about a past habit (children seeing less of their parents) that has now stopped. The idea of overcoming difficulty is totally absent. The second is about a particular purpose involving nursery children.

A further possible reason for misuse of BE USED TO (+ -ing) is the fact that USED TO lacks a present tense form, making it easy to think wrongly that BE USED TO is this form. A present meaning of USED TO must instead be expressed by some such means as the adverb regularly plus an ordinary present tense verb (regularly see). You could even use the past tense form (regularly saw) in place of used to see in (g).

A synonym of BE USED TO is BE ACCUSTOMED TO. The “to” is again prepositional, so that any following verb needs -ing. Sentence (f) would thus be perfectly correct with are accustomed to in place of are used to. 

Another tricky verb with a prepositional to is TURN TO, as in: 

(i) The speaker then turned to describing some problem cases. 

This means that the speaker started doing something new (describing problem cases). If, on the other hand, the other kind of to is used with TURN, a different meaning is expressed: 

(j) The speaker then turned to write on the board. 

The meaning now is that the speaker physically turned his/her body in order to write something behind him/her. The infinitive form to write includes the idea of purpose like in (h).

Now here is an exercise which presents some other verbs with this troublesome preposition to.


EXERCISE (verbs with prepositional “to”): Rewrite each sentence below so it contains the “to” verb(s) given in brackets at the end (followed by “-ing”). Answers are given afterwards. 

1. The government had promised that they would cut taxes. (COMMITTED THEMSELVES TO). 

2. The government did not think it right to cut taxes. (WAS OPPOSED TO) 

3. Children should gradually be shown how to exercise vigorously.  (BE INTRODUCED TO) 

4. Descartes’ Meditationes again discusses the mind-body split. (RETURNS TO) 

5. People who must always sniff glue often fall so low that they steal.  (ARE ADDICTED TO, ARE REDUCED TO) 

6. Do not become a social worker if you do not want to help the poor.  (ARE NOT ATTRACTED TO) 

7. Destroying forests is one way to warm the earth’s atmosphere. (CONTRIBUTES TO) 

8. If a child cannot understand a definition, the teacher may try instead to give examples.  (RESORT TO).




1. The government had committed themselves to cutting taxes.

2. The government was opposed to cutting taxes.

3. Children should gradually be introduced to exercising vigorously.

4. Descartes’ Meditationes returns to discussing the mind-body split.

5. People who are addicted to sniffing glue often are reduced to stealing.

6. Do not become a social worker if you are not attracted to helping the poor.

7. Destroying forests contributes to warming the earth’s atmosphere.

8. If a child cannot understand a definition, the teacher may resort to giving examples.


3 thoughts on “35. “to do” versus “to doing”

  1. I’m not sure all of those “two-word” verbs are actually two-word verbs. They strike me as just regular verbs with a prepositional phrase as a complement. The real two-word verbs have different behaviour when you use a pronoun object. For example, look up can either be look followed by a prepositional phrase that starts with up, or it can be the verb look up. Notice where the pronoun object goes:

    I looked up the word (this is look up + the word)
    I looked it up.
    *I looked up it.

    I looked up the building (this is look + up the building)
    *I looked it up
    I looked up it

    Another way to tell is by deleting the material. Consider sleep in.

    I slept in this morning.
    I slept in.

    I slept in the tent.
    ?*I slept in. (grammatical, but doesn’t mean the same thing anymore)

    In the first case, it’s sleep in plus a complement this morning. In the second case it’s just the verb sleep plus the complement in the tent.

    For these reasons, I wouldn’t say that “look forward to” is a verb. It’s just the verb “look” followed by the adverb “forward”, then a prepositional phrase starting with “to”.

    • Thanks for this. Terminology is so often the bane of language analysis, so let me start by defining my own (which I have borrowed from elsewhere). The verbs I’ve listed in this post are termed “prepositional” because they include a preposition that is said to “belong” to them rather than to the following noun. There is a difference between this kind of preposition and one following an ordinary verb. Compare:

      PREPOSITIONAL VERB: The police will look into the matter.
      ORDINARY VERB: The sun rises in the east.

      My grammar reference book says that the first kind of preposition is predictable when the verb has a particular meaning but the other kind isn’t. Thus, the preposition “into” is fixed when the meaning is investigate, whereas different prepositions are possible with “rise” (= ascend). You could say “rise above the horizon” or “rise before 6.00″.

      The two-word verbs that you mention are what my book calls “phrasal”. The second word in them is not a preposition but an adverb, and that explains why a noun or pronoun can be written before it. The term “two-word” is then used as a generalization for both groups: prepositional and phrasal. I chose to call my verbs “two-word” instead of the more precise “prepositional” because I wanted to keep the English clear and simple, avoiding technical language. Perhaps that was a mistake, though!

      • I agree entirely on your point about terminology. I would also have used the term “phrasal verb”, I think that’s pretty standard actually, but I was trying to stay in line with the terms you used in your post. What was that about tricky terminology again? 🙂

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