Questions & Answers about Mi abuelo es de lo más excéntrico.
How does de lo más function here compared to just saying muy excéntrico?
The phrase de lo más combined with an adjective translates to extremely or highly. It is an absolute superlative, meaning it expresses the highest degree of a quality, similar to adding the suffix -ísimo (excentricísimo). It sounds a bit more expressive and conversational than simply saying muy excéntrico (very eccentric).
If the subject were female (my grandmother), would the adjective excéntrico change to feminine?
Why do we use es instead of está when describing his eccentricity?
We use es from the verb ser because being eccentric is a defining characteristic or a permanent personality trait of the grandfather. If you wanted to emphasize that someone is just acting eccentric at this very moment, you might use está, but excéntrico usually pairs with ser to define a person's nature.
Could I say el más excéntrico instead of de lo más excéntrico?
You could, but it changes the meaning. Saying el más excéntrico is a relative superlative, meaning he is the most eccentric person compared to a specific group (like your family). Using de lo más means he is just extremely eccentric in general, without comparing him to anyone else.