When conjugating adjectives, can we use the normal form of the adjective and use the copula です to indicate its form?


This is specifically for い-adjectives, as な-adjectives work this way.  
For example, when I want to say something is not delicious I'd usually say
**おいしくない**.  
Would it be possible to use **おいしい じゃありません** and would it mean the same thing?




It would mean the same thing, but wrong in terms of grammar.

* * *

おいしくない:

  * Question おいしくない？ (Delicious, isn't it?) valid
  * Statement おいしくない (Not delicious) valid

* * *

おいしいじゃありません:

  * Question おいしいじゃありません？ (Delicious, isn't it?) valid
  * Statement おいしいじゃありません **Not valid**

The question "おいしいじゃありません？" is a unique edge case, and you might never use it
in your life.

The statement "おいしいじゃありません" looks/sounds wrong although the message is clear
you are not enjoying that meal.

* * *

Possible statements to deny おいしい:

  * おいし **く** ありません

Following works too:

  * おいしいごはんではありません
  * おいしいとは思いません

* * *

**Edit** :

The above are basics. Hate to add complexity but there is yet another edge
case where one is happy with the meal and say:

  * Statement おいしいじゃありません (Isn't this delicious)
  * Statement おいしいじゃありませんこと (Isn't this delicious)

This carries the same logic as the question, but is not a question. It's
somewhere between a rhetorical question and a firm statement. These are
advanced expressions which may be used with enough context and correct
pronunciation.




It would mean the same thing, but wrong in terms of grammar.

* * *

おいしくない:

  * Question おいしくない？ (Delicious, isn't it?) valid
  * Statement おいしくない (Not delicious) valid

* * *

おいしいじゃありません:

  * Question おいしいじゃありません？ (Delicious, isn't it?) valid
  * Statement おいしいじゃありません **Not valid**

The question "おいしいじゃありません？" is a unique edge case, and you might never use it
in your life.

The statement "おいしいじゃありません" looks/sounds wrong although the message is clear
you are not enjoying that meal.

* * *

Possible statements to deny おいしい:

  * おいし **く** ありません

Following works too:

  * おいしいごはんではありません
  * おいしいとは思いません

* * *

**Edit** :

The above are basics. Hate to add complexity but there is yet another edge
case where one is happy with the meal and say:

  * Statement おいしいじゃありません (Isn't this delicious)
  * Statement おいしいじゃありませんこと (Isn't this delicious)

This carries the same logic as the question, but is not a question. It's
somewhere between a rhetorical question and a firm statement. These are
advanced expressions which may be used with enough context and correct
pronunciation.

