When to use accusative and nominative?

Question

I am having some difficulty figuring out the Latin translation for the following sentences:

1. My favourite animal is a dog. Will dog (canis) be considered as nominative or accusative (canem)?
2. I want a dog. Will it be canis or canem in this case?

I would think that the 'I' in the sentences would be the nominative which would make dog the accusative but I am not sure.

Answer 1

Hugh is absolutely right, but just to add a bit more explanation…

Nominative is the "default case" in Latin. If all else fails, use the nominative. It's also, conveniently, the form listed in dictionaries, and the form people will use when talking about the word itself ("The Latin word for 'lord' is dominus").

Accusative is used when it's the direct object of a verb. In other words, when there's a verb, with a subject, and the subject is doing something to your noun—that's when the noun becomes accusative. Unlike in English, this can even apply to verbs with passive forms, like Marcus sequitur canem, "Marcus is following the dog".

In your first sentence, nothing is happening to the dog: the verb "is" doesn't represent any sort of action. Since nothing is making the noun accusative, it'll remain nominative.

In your second sentence, though, the verb "want" is happening to the dog. It's a direct object, so it becomes accusative.

Note that, as Joonas notes, these aren't quite the same rules as in English! In English, any verb makes a following noun accusative, even verbs like "is": consider "he is my favorite person" versus "my favorite person is him". If you ever hear an exchange like "Is Alex here?" "This is he.", that's a prescriptivist Latin influence rearing its head.

Answer 2

1. My favourite animal is a dog.

Dog will be canis, nominative because 'is' isn't a transitive verb, it's a copular. However (just to confuse you) Animal mihi gratiosum, the subject, is also nominative; the nominative ends in -um because animal is neuter.

2. I want a dog.

This is a straightforward transitive verb; the subject if it is stated, will be nominative - 'ego;' the object will be accusative except after egeo

ěgěo (followed by Genitive or ablative) cănis, I need a dog;
cănem fingo, I would like a dog; (unlikely)
cănem spero, I hope for a dog.

Answer 3

Hugh's answer is good and correct, but let me offer you a different point of view.

English makes a distinction between nominative and accusative only for some pronouns. The nominatives (I, he, she) are used in different situations than accusatives (me, him, her). Latin and English use the two cases quite similarly, and in simple sentences like your examples the correspondence is excellent.

So: To figure out which case to use, write the sentence in English with the noun replaced by a pronoun. The correct English form of the pronoun tells you which case to use in Latin. I repeat that this is not infallible, but a good rule of thumb.

Using your examples with a pronoun, we have:

1. He is my favourite animal. (Nominative!)

2. I want him. (Accusative!)

English uses the cases weirdly with "be". In "it is he/him" many would choose "him", whereas Latin requires nominative. (This is why I reworded your first example! In the original form the rule of thumb would indeed suggest accusative.) Perhaps it would be a good supplement to this rule of thumb that the verb esse needs nominative.