Foot is a noun here, not an adverb:
- I can barely see a foot in front of me in this fog.
So the direct answer to your main question of “Can a noun be an
adverb?” is no, because a word cannot ever be both a noun and also an
adverb — at the same time.
We know it’s a noun because it takes an article: a foot, meaning one foot. You cannot do that with adverbs. Adverbs can take very, but you could not say that you can barely see *very foot in front of you. That’s ungrammatical because foot is not an adverb. It’s a noun.
But at different times? Sure! It’s perfectly normal for the same-spelt
word to serve as a different part of speech in one sentence than in
other, dissimilar sentences. For example, fast can be a noun or a verb or an
adjective or an adverb — provided these are in four different sentences.
Although quite honestly, I can't imagine a scenario under which foot
could ever be an adverb. It’s almost always a noun, at least until it
comes time for you to foot the bill.
However, that’s not what’s happening in your sentence. In the same
way that the to in to foot tells you that the word foot is probably
being used as a verb in my footing-the-bill sentence, the words around
foot in your sentence give away that it must be a noun.
you know that foot is definitely a noun because it’s the head of the
noun phrase (hereafter abbreviated NP) “a foot in front of me”.
That NP begins with the indefinite article a in the NP’s determiner slot.
Syntactically, the NP “a foot in front of me” is composed of
the same sorts of components as in the NP “a hand in front of me”
or “a wire in front of me”. Imagine this sentence:
The fog was so thick that I couldn't see a branch in front of me
until it smacked me in the face.
- see a foot in front of me
- see a branch in front of me
You have a noun phrase with an article, the head noun, and
a prepositional phrase further describing that noun.
But in the branch case, that NP is serving the grammatical role of being
the verb see’s direct object. As you correctly observed, that’s not
what’s happening in your own sentence: nobody is seeing a foot. The
grammatical role of your NP is instead adverbial. It says where you
could barely see, not what you could barely see.
When the NP is acting as a verb’s direct object, it is not “modifying”
that verb. A verb’s arguments (such as its subject or its various objects) are not considered to be “modifiers” of that verb. They’re just arguments, not modifiers.
With the sentence that has the NP *“a branch in front of me”, if you exchange that whole NP with the pronoun him,
you still have an NP acting as the verb’s direct object:
- I could barely see a branch in front of me in the fog.
- I could barely see him standing right in front of me in the fog.
That's because the overall syntactic role of the NP has not changed, even
though him is a different part of speech than branch is. Neither of
those is “modifying” the verb; they are not acting adverbially. They’re just serving as the direct object, as an argument.
But your NP is not the verb’s direct object. Instead it is being used
to describe the verb just as any other adverbial expression might. Here
are several syntactically equivalent examples:
- I couldn’t see a foot in front of me in the fog.
- I couldn’t see very far in the fog.
- I couldn’t see clearly in the fog.
- I couldn’t see well in the fog.
Each constituent (that is, each sentence element) there which I’ve marked in bold is syntactically
equivalent — because each of those four is an adverbial use.
That is not the same thing as saying that each one is an adverb!
Parts of speech apply only to single words, never to longer phrases.
So you can’t say that very far “is” an adverb. It isn't. It's an
adverbial phrase. Here in very far, far actually is an adverb, but
in a a foot, the word foot is just a noun. If it were an adverb,
it would forbid determiners like a and accept the adverb very as
a modifier, but it does not.
Here’s another example:
- He called me often.
- He called me quickly.
- He called me the first Friday of every month.
Although often and quickly are adverbs, the NP “the first Friday of
every month” certainly is not. But we can use that NP as an adverbial
modifer of the verb call.
It’s important not to confuse syntactic roles with parts of speech. You
have to look at the larger grammar of the sentence to see that entire
multiword phrases can act as interchangeable syntactic constituents just as
much as a single word can be such. The Wikpedia article on
In English, adverbials most commonly take the form of adverbs, adverb
phrases, temporal noun phrases or prepositional phrases. Many types of
adverbials (for instance: reason and condition) are often expressed by
- James answered immediately. (adverb)
- James answered in English. (prepositional phrase)
- James answered this morning. (noun phrase)
- James answered in English because he had a foreign visitor. (adverbial clause)
An adverbial is a construction which modifies or describes verbs. When an
adverbial modifies a verb, it changes the meaning of that verb. Word
groups, which are also considered to be adverbials, can also modify verbs:
for example, a prepositional phrase, a noun phrase, a finite clause or a
There are no adverbs in the NP this morning, only a demonstrative and a
noun, but the entire phrase is still being used as an adverbial syntactic
constituent just as much as the adverb immediately was.
This is the same class of confusion as we see when people mistakenly call
- Giving me a ride home saved my life that day.
- Friends saved my life that day.
- She saved my life that day.
- How and when I left saved my life that day.
There you see various different types of NPs, each acting as the subject of
the verb saved. Sure, friends is a noun, but she is a pronoun not a
noun — and giving is a verb not a noun. That doesn’t mean those NPs can’t
all be subjects. They can and are. They just aren’t all nouns is all.
Same with you and adverbs versus adverbials.
Just like how the NP “giving me a ride” is not an actual noun, your NP of
“a foot in front of me” is not an actual adverb. That doesn't stop them
from serving as syntactic constituents in grammatical roles that in other
sentences could be filled by a single word of the appropropriate part of
speech. They’re always still noun phrases, not nouns or adverbs.