Here's why:
* Common ancestor: Both Sardinian and Italian are Romance languages, descended from Vulgar Latin, the spoken language of the Roman Empire.
* Limited influence: Sardinian has been relatively isolated from other Romance languages, meaning it retained more of the features of Vulgar Latin. This makes it less influenced by later developments that shaped Italian.
* Vocabulary and grammar: Sardinian shares a high degree of vocabulary and grammatical similarities with Italian, making it easier for speakers of one to understand the other.
However, it's important to note that while Sardinian is the closest, there are other Romance languages that are also quite similar to Italian, such as:
* Spanish: Shares a large vocabulary and many grammatical features with Italian.
* French: Despite greater differences, has some similarities in pronunciation and grammar.
* Romanian: Also a Romance language, shares some similarities with Italian, especially in vocabulary.
Ultimately, the "closest" language is subjective, as it depends on the specific criteria you're using to define closeness.