Causative constructions are used to talk about actions which we do not do personally, but ask or pay somebody else to do for us.
Why do people go to see a dentist? To repair or check their teeth? No. People go to a dentist to have or get their teeth checked or repaired by a dentist.
When we do not perform an action ourselves but instead cause the action to be performed by another person, we describe the fact with a 'causative' construction. The causative is constructed by combining a conjugated form of the verb 'to have' or 'to get' with the main verb past participle.
The full construction is usually:
'To have' (conjugated) + direct object (noun or pronoun) + verb past participle
'To get' (conjugated) + direct object (noun or pronoun) + verb past participle
I'm having my house painted. (I paid another person to paint my house.)
I had my car repaired after the accident. (I paid another person to repair my car.)
I got my hair cut yesterday. (I paid the hairdresser to cut my hair.)
I'm getting my hair cut tomorrow. (I will pay the hairdresser to cut my hair.)
Identifying the agent of an action
Similar to the Passive voice, it is not necessary to identify the agent of an action (the person or thing that performs the action). We can identify the agent in two ways:
A: 'to have' + direct object + verb past participle + 'by' + agent (usually a noun):
I had my hair cut by Pauline.
I'm having my house built by Barrett Homes.
B: 'to have' + agent (as a direct object noun or pronoun) + verb infinitive + object (as a direct object noun or pronoun). In spoken English, the verb 'to get' often replaces 'to have', and in this case, 'to' is added to the infinitive.
The teacher had his students write an essay.
The teacher got his students to write an essay.
I had him do it.
I got him to do it.