1. He had dinner with his family.

2. He had a light dinner today.
3. He had a heavy dinner today.
4. He had a good dinner today.
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In #1, we do not use an article before 'dinner.' What about the others? Why do we have to put 'a' before the structure 'adjective + dinner'?

In English, the use of articles before nouns can depend on the context and the specific case. Let's look at the examples you provided:

1. "He had dinner with his family."
Here, the noun "dinner" is used generically to refer to the activity of having the main meal of the day. In this case, "dinner" is being used as an uncountable noun, so we don't use an article.

2. "He had a light dinner today."
In this case, "light" is an adjective describing the type or quality of dinner he had. When you use an adjective to describe a noun, it's common to use the indefinite article "a" before it.

3. "He had a heavy dinner today."
Similarly, "heavy" is an adjective describing the type or quality of dinner. So, we use the indefinite article "a" before it.

4. "He had a good dinner today."
Once again, "good" is an adjective describing the quality of dinner. Therefore, we use the indefinite article "a" before it.

In summary, when you use an adjective to describe a noun, it is typical to include the indefinite article "a" before the adjective-noun phrase. However, in cases where "dinner" is used as a generic activity, as in the first example, we do not use an article.

In English, the use of articles (a, an, the) is often dependent on the context and the specific noun being modified. Let's break down the different sentences you provided to understand why the articles are used or not used.

1. "He had dinner with his family."
In this sentence, the word "dinner" is being used as a general, uncountable noun. When referring to meals in general, we do not usually use an article. It's similar to saying "He had breakfast" or "He had lunch." Since it is not specifying a particular dinner, no article is needed.

2. "He had a light dinner today."
In this sentence, the word "light" is describing the kind of dinner he had. Here, "light" functions as an adjective, modifying the noun "dinner." When using an adjective to describe a noun, it is common to use an indefinite article "a" before the noun. So, "a light dinner" means a dinner that is not heavy or substantial.

3. "He had a heavy dinner today."
Similarly to the previous sentence, "heavy" is an adjective describing the noun "dinner." Again, when using an adjective to describe a noun, we use an indefinite article "a" before the noun. So, "a heavy dinner" means a dinner that is substantial or filling.

4. "He had a good dinner today."
Once again, "good" is an adjective describing the noun "dinner." So, we use the same rule of using an indefinite article "a" before the noun. In this case, "a good dinner" refers to a dinner that was enjoyable, tasty, or satisfying.

In summary, the use of the article "a" before an adjective + noun structure (e.g., "a light dinner," "a heavy dinner") is because the adjective is describing the specific kind or quality of the noun.