Do I eat anymore?

Since I always eat dinner, why do we at the present moment may say in any of the three tenses:
-- I eat dinner.
-- I have eaten dinner.
-- I ate dinner.

Your opinion is welcome.

I am eating

I am having my dinner

If it is the present tense, the present moment and I am eating my dinner:

"I'm having my dinner" (most usual for me anyway in such situation)
or simply "I'm having dinner".
"I'm eating dinner" ... well, ok, but not the most usual. Speaking personally.

For me "I'm eating dinner" would be what I'd say if someone called me in the middle of dinner and asked me what I was doing.

I'd be more likely to say "I'm having dinner" if I were telling someone where I'd be dining: "I'm having dinner over at the Antimoon Steakhouse."

Hey sounds a cool restaurant, mjd! Would you make a reservation for me this weekend, please? I'm a veggie though!

Similar examples can be found in many places. As we know "the sun rises in the east" is a permanence that will not end, I don't know why we can say in any of the three tenses:
1a: The sun rises in the east.
1b: The sun has risen in the east.
1c: The sun rose in the east.

Again, as Tom goes to school every day, we may still say it in any one of them:
2a: Tom goes to school.
2b: Tom has gone to school.
2c: Tom went to school.

Since Simple Past denotes a past happening, why shall we possibly use it to speak of a permanence or routine that has not yet ended?

The progressive tense "I'm eating dinner" is also a good example. It can also refer to the routine. But we are told that we shall use Simple Present to refer to a routine, not the progressive.

THE BEGINNING OF THE CONFUSION

In the beginning of learning English tense, we students in young days had to accept the injudicious process to fill in the ‘right’ tense:
Ex: Tommy (go) to school every day.
== Even on internet, today one can easily find many such exercises to help young students to get into the first step of English tense.

In school, teacher will help students a bit, I am sure. “Do you see the implication of a habit here? Yes? Good. So we fill in Simple Present goes, with the suffix -es, because Simple Present expresses habit.” And students will do it accordingly. They usually don’t ask much.

But I don't know about Adult Education. I estimate an adult would have enough common sense to ask, “if from the sentence I have already seen the meaning of habit, why shall we redundantly use Simple Present tense to say it again?”

The adult is right in hitting the point. It is redundant to use Simple Present to repeat what has been already implied by the sentence. As most learners don’t recognize, this is the first step to error, even a big one, and yet any learner has to accept it. To be worse, after the adult has accepted the idea of using Simple Present to express habit, in later days she or he will totally forget that, at the very first, we have understood a case of Habit based on the sentence, rather than on the tense. Now the role of the sentence is totally ignored. The meaning of the sentence has been shifted to the tense only. Most often, as we may reasonably suspect, when we are discussing the tense, are we really talking about the tense, or the sentence?

Do we really know the implication of habit from this structure:
Ex: Tommy (go) to school every day.
Or from the tense, which is only a suffix -es, or sometimes nothing at all?

In all discussions about tenses over internet, I must say people completely ignore the role of sentence. I have always pointed out and proven that, as we think we talk about the meaning of a tense, we are actually discussing the meaning of the sentence.

As a student usually doesn't know, while he or she fills in the tense for "Tommy (go) to school every day", he has invited to embark the big confusion, mistaking that the tense says what the sentence says. Unfortunately, now most of the explanations of tenses are based on this confusion. I am not predicting their reasoning will finally collapse, but I will predict no further knowledge will be built on this confusion. I have always asked this to readers: do you know how many concrete rules we have had on English tenses so far? Maybe to your surprise, there is only one: "Present Perfect doesn't stay with past time expressions, such as yesterday". However, as we shall see later, even this rule is barely acceptable. There is no one concrete rule in present-day tenses explanations. But more falsities have to be created to cover the consequence of this sentence-tense confusion.

FORBIDDEN KNOWLEDGE: The Past Family

The enthusiasm wherein I have spent ample time to study English tenses was triggered off by one phenomenon. In explaining tenses, most grammar writers have to hide away the family of past time adverbial “in the past xx years”, which I call the Past Family, (such as "in the past, in the past year, in the past two months, during the past three decades, over the past four weeks, for the past few years", etc.) These past time adverbials stay with Present Perfect:
Ex: They have worked here in the past few years.

Intentionally or unintentionally avoiding them, grammarians may easily attain a fraudulent conclusion: “Present Perfect doesn’t stay with past time expressions”. Obviously, if they talk about the Past Family in their books, they cannot reach such a conclusion. (Actually, they also hide away time expressions like "before, previously, earlier", etc., any time adverbials that denote past time.) The falsity is based on young students’ trust in them. Grammarians make full use of the inexperience and successfully avoid to talk about a lot of time adverbs.

If this year is 2004, then “since 2000” is same as “in the past (2004-2000=4) four years”. If SINCE 2000 prefers Present Perfect, so shall “in the past four years”.

Nowadays many Asian English users, as well as some English native speakers, wrongly choose Simple Past for these past time adverbials, because they follow the rule that “Present Perfect doesn’t stay with past time expression”. Not to talk about the Past Family is an oversimplification. And yet, to produce a conclusion that depends on the disappearance of the Past Family, is universally not acceptable. It is neither study nor research at all. Deliberately giving a wrong conclusion, grammar writers have built up a more ethical than grammatical problem. Where is the righteousness in doing so? Nowadays, nonetheless, this kind of infamous avoidance has become an indispensable part of present-day grammars.

Some readers on various forums didn’t believe grammar writers would deliberately do the hide-away. I explained it is hard to believe, but it is true. It is not an isolated case but a part of the big confusion. I challenged if they could find a book that talks about the Past Family. If not, why? I pointed out a common and famous grammar book for example. It was written by a group of editors who had scanned over thousands of readings and magazines. They claim REAL examples in their book. And yet they all missed to find an example of the Past Family. Can’t we see it is a kind of forbidden knowledge?

THE EMBARRASSMENT OF DEFINITE PAST TIME ADVERBIALS (DPTA)

Most grammar authors will remind you of the ‘Golden Rule’: Present Perfect doesn't stay with past time expressions, such as yesterday, in 1993, last week, etc. They are Definite Past Time Adverbials (DPTA). However, as they know by heart they are hiding away many past time adverbials like "in the past xx years", they would not tell you clearly how to define DPTA. Defining DPTA to students is showing the weakest point for students to pinpoint the error in the ‘Golden Rule’. Therefore, in an area where grammar writers can spend a lot of time in collecting and defining data easily, they tell us the least of the fact. What a shame. Any of us will meet past time adverbials much more than any grammar book can possibly show you. Most of us don’t even know why.

Challenge my words and double check it. For grammar writers to define DPTA inattentively is not an isolated case. The obvious purpose is to protect what they are hiding away. I am not asking grammar writers to make a comprehensive collection of DPTA. I am pointing out they haven’t started the first step to define them. As students inevitably have to use the Past Family (such as “in the past xx years”) to express, defining DPTA correctly and clearly is encouraging them to ask why the Past Family can stay with Present Perfect. This will instantly kill the only and the last rule in English tense: Present Perfect doesn’t stay with past time adverbials.

We discover and remember what DPTAs are totally by ourselves in observing what usual writers use to connect to Simple Past. We didn’t acquire them through reasonable descriptions. Even with searching machines on internet, we cannot find its solid definitions. The best result we can get is something like “.....Definite Past Time Adverbials such as yesterday, in 1993, last week, etc.” Have you ever seen in any grammar the contrast between Specific Past Time and Unspecific Past Time? How did they say?

English tenses explanation has been undesirable. With so many concealments and omissions, it has now become more of a moral problem than merely a grammatical one. We really cannot choose highly selected examples to make a twisted conclusion. We cannot hide away past time adverbials for Present Perfect and then preach that Present Perfect doesn’t stay with past time adverbials. If confronted, they will create difficult terms in their instant unreadable theory, without any hesitation. After making so many false ideas, they won’t hesitate to create one more.

You can also say "I'm having dinner tonight" cause tonight is a present progressive time expression

Yes, this is the beauty of English tense. You can say anything about a tense. It is an absolute freedom. Grammars say Simple Present expresses routine or habit. It is not true. They want to restrict our freedom. Actually there is no rule at all. Tell me if there is one.