Tenses logic understanding

Solution 1:

The verb "do" has many functions. It can be a simple verb with the meaning "to make happen", "to perform" (a task):

I'm going to do the washing up.

I'm going to do the shopping.

As an auxiliary verb in a positive sentence it emphasises it:

unemphasised: I play this game.

emphasised: I do play this game.

It's usually only used in this way following a previous statement casting doubt on it:

You don't play this game, do you?

I do play this game.

As an auxiliary verb in a negative sentence with "not" it provides "do" support:

unidiomatic: *I play not this game.

idiomatic: I do not play this game.

idiomatic: I don't play this game.

The asterisk (*) indicates that the grammar in the sentence is not idiomatic in modern English. It used to be idiomatic which is why you'll see it in old texts. Now it is still understood but it sounds very old fashioned. Many people associate it with Biblical language.

"do" support is necessary in negative sentences with "not" which would only have a single verb for the subject otherwise. So the positive sentence:

I played this game.

becomes the negative sentence:

I did not play this game.

I didn't play this game.

Another use is for asking some types of question:

unidiomatic: *Play you this game?

idiomatic: Do you play this game?

unidiomatic: *Play you not this game?

idiomatic: Do you not play this game?

idiomatic: Don't you play this game?

The use of "do" is optional for "have" (as a regular verb meaning "possess") in some varieties of English:

Regular "have": I haven't a clue.

Auxiliary "do", Regular "have": I don't have a clue.

Auxiliary "have", Regular "get": I haven't got a clue.

As an auxiliary verb, "have" doesn't use "do":

I have played this game.

I haven't played this game.