Learn English Grammar: When to Use the Word "Had"?

The word "had" serves two functions in English: as the past tense of "has/have", but also as a "helping verb" that is added to the past participle of a verb to create another tense, the past perfect. 

Let's look at the following examples:

1. She has a book. She had a book. 

This simply shows the use of the verb "to have" which means "to possess", in its present and past tense.

2. She writes a book. She wrote a book. She has written a book. She had written a book. 

This one shows the present and past tense (write/wrote), and gives an example of how "has" and "had" both act as "helping verbs" when added to the past participle (written) in the formation of the present perfect (has written) and the past perfect (had written).

The present perfect tense is used to describe something that happened (she has written a book) or didn't happen (she has never written a book) from the perspective of the current time, which is why it's called the present perfect. In other words, as of now, the present time, she has written a book.

The past perfect tense is used to describe something that happened in the past at a time before another time that is also in the past. So, "By the time Alice was 16 years old, she had written a book". Alice is not currently 16 years old - that happened in the past, which we can tell because of the use of the past tense word "was". But before that, even farther in the past, she wrote a book.

So when do you use "had"? You use it either to show a simple past tense of possession, or as a helper verb to refer to something that happened longer ago in the past from the reference point of something that also happened in the past, but more recently.

More on writing: 
https://bucketofuseful.blogspot.com/2017/10/why-you-should-never-trust-spell-check.html

Image from Pixabay https://pixabay.com/photos/correcting-proof-paper-correction-1870721/