1. There are two Renoirs on the wall.

2. This/That Renoir looks great.
3. Look at the Renoir on the table.
4. A Renoir is hanging on the wall.
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1. In each sentence does 'Renoir' mean Renoir's painting? Are they all grammatical?

2. Do we have to stress the first syllable or the second syllable when we pronounce 'Renoir'?

Yes, it's a short form to refer to one or two of Renoir's paintings. All are grammatically correct.

And yes, the first syllable of "Renoir" is stressed.
http://www.dictionary.com/browse/renoir?s=t
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why

🤔why man

1. In each of the sentences, the word "Renoir" is referring to Renoir's painting. They all use the word "Renoir" as a noun to indicate a specific artwork created by Renoir.

Regarding their grammaticality, while all four sentences are grammatically correct, there are slight differences in their structures:

- Sentence 1: "There are two Renoirs on the wall." Here, "Renoirs" is used as a plural noun, indicating that there are two paintings by Renoir on the wall.
- Sentence 2: "This/That Renoir looks great." This sentence uses "Renoir" as a singular noun, referring to a specific painting that the speaker is pointing out. The use of "this" or "that" before "Renoir" helps to specify the particular painting being referred to.
- Sentence 3: "Look at the Renoir on the table." This sentence uses "Renoir" as a singular noun. It refers to a particular painting on the table that the speaker wants the listener to observe.
- Sentence 4: "A Renoir is hanging on the wall." Here, "Renoir" is used as a singular countable noun, indicating that there is one unidentified painting by Renoir on the wall.

2. The pronunciation of the word "Renoir" typically emphasizes the second syllable, "noir." So, the stress falls on "noir" (rehn-WAHR). However, pronunciation can vary depending on regional accents or individual preferences.