The causative structure is used to show an action done by someone or something other than the subject. It uses a different construction than the traditional SVO/SVC/SVA sentence and can be a little confusing to new users of the language.
Ex: I had the barber cut my hair. (active voice)
I got/had my car fixed. (passive voice)
Jan let Heather borrow her car for the weekend.
The professor made everyone present their findings using a Powerpoint presentation.
The causative, then, introduces an agent as the doer of the action. In other words, the subject is not directly responsible for the main action in the sentence. Moreover, the main action in the sentence is limited to a base or infinitive verb, and as such cannot take a tense, regardless of when the action occurred. Only the causative verb adjusts for time.
The main causative verbs are have, get, make, and let, though there are others which are generally self-explanatory.
Let’s look at the structure:
I had the barber cut my hair.
(sub) (causative verb) (agent) (action verb) (object)
The causative is used to suggest that the subject caused the agent to do the action. The differences are very subtle, but should be understood.
Have—this suggests that the subject asked or paid the agent to do the action on their behalf.
Make—this suggests more of a forced action on the part of the agent.
Get—this has the idea of persuasion or convincing the agent to do something
Let—this is not so much a case of causing, but rather of allowing, or permitting the agent to do something.
Of these four causative verbs, only get uses the infinitive verb (to verb) for the main action (in the active voice). The others use the base verb. Other verbs that can be used with this structure (e.g., allow, help, enable, keep, hold, force, require, persuade) all use the infinitive (except for help, which can use the infinitive or base verb).
Another confusing element of this structure is that the agent does not have to be a person. A thing (a machine, for instance) can be made to do something, as can an animal.
Ex: I’ll have the new software analyze the data and (I will) report back to you.
Would it be possible for you to make the engine rev a little higher at highway speeds?
Betty let her dog Chester run in the park without a leash.
After months of trying, Zack finally got his parrot to say “hello”.
The causative also has its own form of the passive voice. In this construction, the agent is not necessary in many situations (especially when the agent is obvious or unknown):
Ex: I had my hair cut. (by the barber)
subject causative verb object main verb (past participle)
Joseph got his car not only fixed, but also cleaned. (by the mechanic)
We commonly use have and got in the passive voice of the causative, however in certain contexts we might also use allow.
Ex: Mr. Theodore allowed his car to be displayed at the car show for the weekend.
Notice, however, that we rely on the full passive structure, including the infinitive to and the be verb.
The contract requires us to complete the project no later than the 15th of this month.
The money that he made by working overtime enabled him to take care of his urgent debts and have a little breathing room.
Rest assured, Mr. Wilson, we will force you to comply by any legal means at our disposal if it comes down to it.