Need help understanding the placement of 'nicht' [duplicate]

Question

In the sentences:

1)Ist das die Professorin?

-Nein, das ist nicht die Professorin.

Here 'nicht' precedes the definite article 'die'. This is because the noun 'Professorin' is preceded by 'die'

2)Siehst du den Stuhl?

-Ich sehe den Stuhl nicht.

Here 'nicht' is placed at the end of the sentence because 'Stuhl' is the object in the sentence.

[Ref:https://resources.german.lsa.umich.edu/grammatik/nicht/ https://deutsch.lingolia.com/en/grammar/sentence-structure/negation https://www.thoughtco.com/the-position-of-nicht-1444481]

In sentence_1 why can't we place nicht at the end of the sentence as 'Professorin' is the object in the sentence .i.e. why is 'Nein, das ist die Profesorin nicht' wrong?

In sentence_2 why can't we place 'nicht' before 'die Stuhl' as the noun 'Stuhl' is preceded by definite article 'die' .i.e. why is 'Ich sehe nicht den Stuhl' wrong?

Thank you for your time and thoughs.

Answer 1

The "nicht" has different targets in the two words. In the first sentence the "nicht" negates the Professor. In the second sentence it negates the verb "sehen". So saying "Ich sehe nicht den Stuhl" would be mean something like "I see the not chair" which makes no sense. One could argue logically the German sentence should be "Ich nicht sehe den Stuhl" but languagre is not always logical.

Answer 2

There is a subtle difference in focus between these sentences.

The sentence "Ich sehe den Stuhl nicht" is simply the negation of the statement "Ich sehe den Stuhl". It says that it is not the case that one sees the chair.

In the sentence "Das ist nicht die Professorin" says that the person is not the professor (but someone else). So the focus is on the person, not on the entire statement. Because of this, Professorin is negated, and nicht is in front of Professorin.