What is the difference between "new puppy" and "a new puppy"?
Take this sentence for example:
My brother’s daughter and new puppy are already best buds
What if we add an indefinite article berere "new puppy", how that would change the meaning of the sentence? Like that:
My brother’s daughter and a new puppy are already best buds
Would that mean that there are more than one new puppy and only one of them is my brother's daughter's best bud?
In the first sentence both the daughter and the puppy are your brother's.
In the second sentence it's not established that puppy belongs to your brother and/or his daughter. "A puppy" might be your brother's, but it might as well be their neighbor's.
If you wanted to say that there were more than one new puppy and only one of them is my brother's daughter's best bud you might say
My brother’s daughter and one of the new puppies are already best buds.
"My brother’s daughter and new puppy are already best buds". Both the daughter and the puppy are your brother's here.
"My brother’s daughter and a new puppy are already best buds". Here, only the daughter is your brother's and the dog is not. 'A new puppy' refers to any puppy that has come into your lives (for example your daughter goes to school and there is a new puppy there).
In relation to your comment of 'Would that mean that there are more than one new puppy and only one of them is my brother's daughter's best bud?', I personally feel that this is not correct. If you wanted to talk about the fact that your brother's daughter is best buds with a puppy that your brother has (out of many) then you would say 'one of the puppies'; "My brother's daughter is already best buds with one of the new puppies"
