Difference between Has/Have and Had
The two words are verbs that we constantly use. In some contexts, they perform the function of a main verb, while in others they are auxiliary verbs. An auxiliary verb is one that helps other verbs, heling them to make sense especially in terms of grammar.
In the sentences below ‘has’ and ‘had’ are main verbs:
She has a pen.
She had a pen.
John has three pens.
John had three pens.
In the four sentences, the only verbs (main verbs) present are ‘has’ and ‘had’. But in the following, they are auxiliary:
She has gone.
She had gone.
John has washed the car.
John had washed the car.
In the clauses ‘has’ and ‘had’ now help the main verbs ‘gone’ and ‘washed’.
Whatever has been said about “has” applies to “have”. The only difference between them is that while we use ‘has’ with he, she, it, each, everyone, someone, somebody etc.; and with singular nouns such as Kelvin, January, war etc., we use ‘have’ with I, you, we, they and plural nouns like boys, trees, Sundays:
He has a pen.
She has a pen.
It has gone.
Ngozi has gone.
I have a pen.
You have a pen
They have a pen
We have a pen.
Ngozi and Johnson have pens.
Now, what is the difference between has/have and had?
The first major difference is that has/have expresses a present action while had expresses the past.
She has a pen (currently).
I have a pen (currently).
She had a pen (before/in the past).
I had a pen (before).
The second difference is that has/have states an action that started in the past and lingers till the present. In the case of ‘had’, it expresses an action that took place in the past before another one began:
I have started writing. (Present Perfect}
She has started writing. (Present Perfect)
She had started writing (before I left the office. (Past Perfect.)
They had set out before rain began to fall.
This is a major difference between has/have and had. You need to master it so that you do not mix them up.