What's the difference between そうだ and そうです?


It supposedly mean "that is so; that is right", but is there any difference
between そうだ and そうです in terms of the context or any point of view?




There is no difference semantically between です and だ. The only differences are
the usage and the politeness.

**The politeness**

Basically in Japanese there are multiple level of politeness, I will only list
the more commons to keep it simple, because a lot of levels of politeness
depend a lot on the person's point of view (like what is considered rude?
etc.).

The two main categories are the 敬語 (けいご : honorific language) and what we
could call the 普通語 (ふつうご : normal language). There are more specific terms but
I'm not going to go in the details.

The 敬語 can be divided in 3 sub-categories:

  1. 尊敬語 (そんけいご : honorific language)
  2. 謙譲語 (けんじょうご : humble language)
  3. 丁寧語 (ていねいご : polite language)

Some people would argue that 丁寧語 isn't part of the 敬語, but that's another
story. I personally see it as 敬語 when explaining it because there's no point
in debating whether polite = honorific or not here.

Back to です and だ, they are what we call copulas and basically they are nothing
more than contractions. だ directly comes from である and です from であります. (で being
a particle)

ある as you must have learned already is the plain form of the verb (辞書形/じしょけい :
dictionary form) which basically is 普通語 and adding ます to the 連用形 (れんようけい/one
of the different verb conjugations in Japanese) of ある (so あり) makes it be 丁寧語
(polite language).

So we can say that だ : 普通語 and です : 丁寧語.

**The usage**

There is not much difference between だ and です in terms of usage. But there are
things you may want to keep in mind:

  * Politeness in Japanese **should** always be determined by the last verb of the **sentence** (and not of the proposition). So if you want to use です, you will want to end the sentence right after. That is a general rule for any verb that is in the polite form. But you know how Japanese people are when being polite, always overdoing things so don't be surprised if you see random polite forms in the middle of a sentence. (like a て form on a verb in 丁寧語...) It is actually very common. 
  * Some particles are not valid when used after だ whereas it is fine to use them with です. For example ので: It is common to see ですので in polite situations, but you will **never** see だので (the correct way to say it is なので).
  * だ cannot be used after an i-adjective whereas です can. 優しいだ → 優しいです. If you want to use an i-adjective in its plain form (辞書形), just use the adjective without copula: 優しい because i-adjectives act like verbs in their plain form. 

Feel free to edit my answer if you have something else in mind, that's all I
can think of at the moment.




There is no difference semantically between です and だ. The only differences are
the usage and the politeness.

**The politeness**

Basically in Japanese there are multiple level of politeness, I will only list
the more commons to keep it simple, because a lot of levels of politeness
depend a lot on the person's point of view (like what is considered rude?
etc.).

The two main categories are the 敬語 (けいご : honorific language) and what we
could call the 普通語 (ふつうご : normal language). There are more specific terms but
I'm not going to go in the details.

The 敬語 can be divided in 3 sub-categories:

  1. 尊敬語 (そんけいご : honorific language)
  2. 謙譲語 (けんじょうご : humble language)
  3. 丁寧語 (ていねいご : polite language)

Some people would argue that 丁寧語 isn't part of the 敬語, but that's another
story. I personally see it as 敬語 when explaining it because there's no point
in debating whether polite = honorific or not here.

Back to です and だ, they are what we call copulas and basically they are nothing
more than contractions. だ directly comes from である and です from であります. (で being
a particle)

ある as you must have learned already is the plain form of the verb (辞書形/じしょけい :
dictionary form) which basically is 普通語 and adding ます to the 連用形 (れんようけい/one
of the different verb conjugations in Japanese) of ある (so あり) makes it be 丁寧語
(polite language).

So we can say that だ : 普通語 and です : 丁寧語.

**The usage**

There is not much difference between だ and です in terms of usage. But there are
things you may want to keep in mind:

  * Politeness in Japanese **should** always be determined by the last verb of the **sentence** (and not of the proposition). So if you want to use です, you will want to end the sentence right after. That is a general rule for any verb that is in the polite form. But you know how Japanese people are when being polite, always overdoing things so don't be surprised if you see random polite forms in the middle of a sentence. (like a て form on a verb in 丁寧語...) It is actually very common. 
  * Some particles are not valid when used after だ whereas it is fine to use them with です. For example ので: It is common to see ですので in polite situations, but you will **never** see だので (the correct way to say it is なので).
  * だ cannot be used after an i-adjective whereas です can. 優しいだ → 優しいです. If you want to use an i-adjective in its plain form (辞書形), just use the adjective without copula: 優しい because i-adjectives act like verbs in their plain form. 

Feel free to edit my answer if you have something else in mind, that's all I
can think of at the moment.

