Can you add です after a plain form of a verb?


In the lyric of イノコリ先生, there is a phrase that surprised me. It goes like :
手を上げられないです。does this mean です can come after verb? such as 来られるです. What if the
verb is polite? Should you add です or not? 来られます。来られますです(?). What is the
difference between 来られるです and 来られます? Does it is restricted only for potential
form verbs?




The short answer:

You can think of です as performing several funcitons. Being a polite form of
the copula だ, or being an auxiliary polite helper verb.

です as a politeness helper verb:

  * No you cannot say 来られるです. The polite present form of the verb is 来られます.   
**You can only append です as a politeness helper for い-adjectives, so 来ないです is
fine because ～ない is syntactically a い-adjective**.

When it is not a polite helper, you only see です when it is **needed to express
past tense** in 来られません **でした**. Politeness is already accounted for by the
helper verb ます. In the present tense you do not say 来られますです.

* * *

The long answer is to look at the conjugation rules of verbs and of
い-adjectives.

For **verbs** , their politeness conjugation uses the helper verb ます. The
conjugation scheme is as follows: [![Verb
Conjugation](https://i.stack.imgur.com/e2S6T.png)](https://i.stack.imgur.com/e2S6T.png)

You may be slightly confused with the い-adjective conjugation scheme, which
can use です as its politeness helper highlighted in yellow below:

[![i-adj
conjugation](https://i.stack.imgur.com/AERdP.png)](https://i.stack.imgur.com/AERdP.png)

As a result you see that there are two negative polite forms. So for example
you can have 暑くないです・暑くありません and their past forms 暑くなかったです・暑くありませんでした where we
note that でした accounts for past tense and ません has already accounted for
politeness in 暑くありませんでした.

Now to complete the earlier table for verbs, we note that **ない is
syntactically a い-adjective** and obeys the conjugation rules for
い-adjectives. So now for **verbs** we have:

[![Completed Verb Conjugation
Table](https://i.stack.imgur.com/b5nkx.png)](https://i.stack.imgur.com/b5nkx.png)

This is why you see 上げられないです, but you cannot get 来られますです or 来られるです.




The short answer:

You can think of です as performing several funcitons. Being a polite form of
the copula だ, or being an auxiliary polite helper verb.

です as a politeness helper verb:

  * No you cannot say 来られるです. The polite present form of the verb is 来られます.   
**You can only append です as a politeness helper for い-adjectives, so 来ないです is
fine because ～ない is syntactically a い-adjective**.

When it is not a polite helper, you only see です when it is **needed to express
past tense** in 来られません **でした**. Politeness is already accounted for by the
helper verb ます. In the present tense you do not say 来られますです.

* * *

The long answer is to look at the conjugation rules of verbs and of
い-adjectives.

For **verbs** , their politeness conjugation uses the helper verb ます. The
conjugation scheme is as follows: [![Verb
Conjugation](https://i.stack.imgur.com/e2S6T.png)](https://i.stack.imgur.com/e2S6T.png)

You may be slightly confused with the い-adjective conjugation scheme, which
can use です as its politeness helper highlighted in yellow below:

[![i-adj
conjugation](https://i.stack.imgur.com/AERdP.png)](https://i.stack.imgur.com/AERdP.png)

As a result you see that there are two negative polite forms. So for example
you can have 暑くないです・暑くありません and their past forms 暑くなかったです・暑くありませんでした where we
note that でした accounts for past tense and ません has already accounted for
politeness in 暑くありませんでした.

Now to complete the earlier table for verbs, we note that **ない is
syntactically a い-adjective** and obeys the conjugation rules for
い-adjectives. So now for **verbs** we have:

[![Completed Verb Conjugation
Table](https://i.stack.imgur.com/b5nkx.png)](https://i.stack.imgur.com/b5nkx.png)

This is why you see 上げられないです, but you cannot get 来られますです or 来られるです.

