What is the difference between "is having" and "has" in this sentence? [duplicate]

A visualization of what we mean in English by the various tenses:

For the sake of presenting the information in another way:

I eat

habitually; in general.

• “I eat venison occasionally.”

as a command

• “Now, we eat!”

I am eating

at this point; at this point, continuously; at a point in the future.

• “I am eating these leftovers. Would you like some?”

• “I am eating lunch with John on Thursday.”

I ate

at a point in the past.

• “I ate squid once.”

• “I ate lunch early today.”

I was eating

at a point in the past, continuously.

• “I was eating my dinner, when the phone rang.”

I have eaten

at a point in the past; in the past in general.

• “I have eaten many different kinds of sushi.”

I have been eating

up to and including now, continuously. = I was and am eating.

• “I have been eating the bread that's on the counter, not knowing it's mouldy.”

I had eaten

before a point in the past.

• “I had eaten barbecue before, but this steak was better than any I'd ever tasted.”

I had been eating

up to and including a point in the past, continuously.

• “I had been eating breakfast in bed, till I started seeing ants in my room.”

• “I had already been eating for fifteen minutes by the time she showed up.”

I will eat

at a point in the future; in the future in general.

• “I will eat an apple a day from now on.”

• “I will eat dinner with you tomorrow if you want.”

I will be eating

up to and including a point in the future, continuously.

• “I will be eating only a little bit of this cake. You can have the rest.”

I will have eaten

before a point in the future.

• “I will have eaten by the time you get out of work, so we can't eat together.”

I will have been eating

up to and including a point in the future, continuously.

• “I will have been eating a vegetarian diet for twenty years next month.”

My guess is that you read a table something like this:

• Present Simple (I eat)
  • habitually; in general.
  • as a command
• Present Continuous (I am eating
  • at this point
  • at this point, continuously
  • at a point in the future.
• Past Simple (I ate)
  • at a point in the past.
• Past Continuous (I was eating)
  • at a point in the past continuously
• etc...

and found it confusing. Your first instinct (and it's a good one!) was to draw a diagram to make sense of it. But the diagram is just as confusing as the table.

The problem is that our brains just don't work that way. If you ask a typical native speaker to list all the situations where he uses a particular tense, mood & aspect, he'll find it impossible. But if you show him a sentence and ask him to choose the correct tense, mood & aspect, he'll have no trouble. In other words, our mental table of tenses and moods looks more like this:

• habitually, generally
  • I eat cheese.
• habitually, in the past
  • I ate cheese.
  • I would eat cheese.
• making a request
  • Please eat cheese.
  • Could you eat cheese?
  • Would you mind eating cheese?
  • I was wondering whether you would eat some cheese?
• imaginary situation in the future
  • If I eat cheese, I will have cheese in my belly.
• imaginary situations in the past
  • I wish I had eaten cheese.
• etc.

So if you want to make a diagram that is useful to learners of English, you need to take the same approach. That's a tall order! I don't even know that it's possible. I'd love to know about any past attempts.