My grammar book says that you can say "the dog," "a dog" and "dogs" to refer dogs. This book says "dogs" is the most casual and common way of saying that among the three.
So, I wanted to say like this:
Some pets are more popular than others. I think one of them is dogs.
One and is don't seem to fit "dogs." How can I say that properly? "Some of them are dogs"?
*I don't know which tag I should put
You are right, it doesn't fit together right in that form.
Two possibilities:
Some types of pets, such as dogs, are more popular than others.
Some animals are more popular as pets. For example, dogs are very popular.
The context you provided sort of changes the general rule. Here's the general rule:
One of them is singular, so you can't use the plural "dogs."
One of them is a dog. or One of them is the dog.
Some of them is plural, so you have to use the plural form "dogs."
Some of them are dogs.
With the context you provided, saying "some of them are dogs" isn't right because you've already said "some pets." So you have to say:
One of them is a dog.
However, even though it violates this rule, you can get away with this:
Some pets are more popular than others. I think one of them is dogs.
You can get away with it because the listener will understand and assume that you're using "dogs" as the name of a category of pets (e.g., dogs, cats, elephants, sheep). This would only be true in informal, spoken English.
The sentence:
Some pets are more popular than others. I think one of them is dogs.
is at best awkward if not grammatically wrong, because it lacks number agreement. One could instead write:
Some pets are more popular than others. I think that dogs are among them.
The answer by Jack O'Flaherty shows some other valid ways to handle this.
When one writes "the dog" (or often "The Dog") to mean the species in general, one is implying that all dogs are the same, at least in the aspects being discussed. For example:
- The Dog evolved from The Wolf.
- The Dog had coexisted with Man for thousands of years.
The late Stephan Jay Gould wrote in several essays that he strongly disliked this form of expression, because it denied or trivialized the real and important differences between individuals. He disliked it even more when applied to larger groups, as for example "The fish is a primitive organism." or "The ape proved an evolutionary dead end." I agree. Thus I advise avoiding this form of expression. Also it can sound pompous and stuffy.
When one writes "a dog" to mean dogs in general, one is implicitly writing of a typical dog. This is neither more nor less formal that using "dogs", but it can also have the problem of ignoring or minimizing variation between dogs, although not as much so as using "the dog".
