What is the reason leading to the difference in tense used for affirmative and negative statements in the construction V~ほうがいい


In the construction of a suggestion statement with V~ほうがいい, the past (perfect)
tense is used for the affirmative (according to
[this](https://japanese.stackexchange.com/questions/56097/what-is-the-
difference-
between-v-%E3%82%8B%E3%81%BB%E3%81%86%E3%81%8C%E3%81%84%E3%81%84-and-v-%E3%81%9F%E3%81%BB%E3%81%86%E3%81%8C%E3%81%84%E3%81%84)
and [this](https://japanese.stackexchange.com/questions/24426/in-front-
of-%E3%81%BB%E3%81%86%E3%81%8C%E3%81%84%E3%81%84-is-it-always-past-tense), the
present tense can also be used for general advice), but the present tense is
used for the negative. Why?

e.g.

Affirmative: ご飯を食べ **た** ほうがいいですよ。

Negative: ご飯を食べ **ない** ほうがいいですよ。

why isn't 食べなかった used for the negative form just like in the affirmative
statement?

* * *

Related:

[What is the difference between V-るほうがいい and
V-たほうがいい?](https://japanese.stackexchange.com/questions/56097/what-is-the-
difference-
between-v-%E3%82%8B%E3%81%BB%E3%81%86%E3%81%8C%E3%81%84%E3%81%84-and-v-%E3%81%9F%E3%81%BB%E3%81%86%E3%81%8C%E3%81%84%E3%81%84)

[In front of “ほうがいい,” is it always past
tense?](https://japanese.stackexchange.com/questions/24426/in-front-
of-%E3%81%BB%E3%81%86%E3%81%8C%E3%81%84%E3%81%84-is-it-always-past-tense)




First of all, note that when making a suggestion, it is used the same
construction than when comparing two things (ほうが 方が), because they are being
compared 2 ways of doing things, namely the way how it is done as for now vs
_a better way to do it_ , i. e the _suggested_ way.

After that, think of the ~た ending not as "past" but as "done" or "after", for
example like in「家に帰った時、 ごはんをたべます。」(I have lunch once I've come back home).

Then, think of a suggestion as a guideline to either:

1) reach some desirable outcome or state. I am at A but I want B.

or

2) keep the current state of things. I am at A and I want to keep A.

Let's see both cases.

* * *

1) Affirmative

When suggesting to do something in Japanese, you tell that "How things would
turn out [ **after** an action is carried out and as a result there is a
desirable state] is better". An action must be done **in advance** in order to
reach that desired state, thus it is used 〜た.

e.g. 勉強したほうがいいです → "The way of having studied is good [to pass the exam]" →
Having studied is better → You'd better study.

You are at A (an ignorant who wouldn't pass) and want B (a knowledgeable
person who would pass).

* * *

2) Negative

But what happens when you suggest **not** to do something? In this case there
is no action that triggers the desirable state as a result, but rather the
desirable state is what would be expected to happen if you do not screw it up
by doing something bad or not recommended. Not doing the hindering action must
be ensured during the whole time span indefinitely in order to keep the
desired state in place, thus it is used 〜ない (non-past).

e.g. ケーキを食べないほうがいいです →"The way of not eating cake is good [to keep fit] → "Not
eating cake is better [to keep fit]" → you'd better not eat cake.

You are at A (in good shape) and want to keep A (in good shape).




First of all, note that when making a suggestion, it is used the same
construction than when comparing two things (ほうが 方が), because they are being
compared 2 ways of doing things, namely the way how it is done as for now vs
_a better way to do it_ , i. e the _suggested_ way.

After that, think of the ~た ending not as "past" but as "done" or "after", for
example like in「家に帰った時、 ごはんをたべます。」(I have lunch once I've come back home).

Then, think of a suggestion as a guideline to either:

1) reach some desirable outcome or state. I am at A but I want B.

or

2) keep the current state of things. I am at A and I want to keep A.

Let's see both cases.

* * *

1) Affirmative

When suggesting to do something in Japanese, you tell that "How things would
turn out [ **after** an action is carried out and as a result there is a
desirable state] is better". An action must be done **in advance** in order to
reach that desired state, thus it is used 〜た.

e.g. 勉強したほうがいいです → "The way of having studied is good [to pass the exam]" →
Having studied is better → You'd better study.

You are at A (an ignorant who wouldn't pass) and want B (a knowledgeable
person who would pass).

* * *

2) Negative

But what happens when you suggest **not** to do something? In this case there
is no action that triggers the desirable state as a result, but rather the
desirable state is what would be expected to happen if you do not screw it up
by doing something bad or not recommended. Not doing the hindering action must
be ensured during the whole time span indefinitely in order to keep the
desired state in place, thus it is used 〜ない (non-past).

e.g. ケーキを食べないほうがいいです →"The way of not eating cake is good [to keep fit] → "Not
eating cake is better [to keep fit]" → you'd better not eat cake.

You are at A (in good shape) and want to keep A (in good shape).

