'I am man' or 'I am a man'?

Question

Man can also mean human beings as an uncountable noun, so does that mean I can say:

I am man.

or

Man are not smart.

without the article?

Answer 1

Can I say "I am man"?

An interesting question. The answer is "in the majority of cases, no! In a poem or in a song or in other such context, yes, sometimes".

'Man' as Generic Noun Phrase

When we use man as a noncount noun, we usually speak of humanity as a whole, or of a "prototypical man".

We bow down to the universal laws,
Which never had for man a special clause
Of cruelty or kindness, love or hate...
(James Thomson, The City of Dreadful Night)

This prototypical man has all the properties of anything we would call a human being, except that he (or she) doesn't exist in an individual physical sense, like all real human beings do.

When we use a word in this way, this is called "generic reference". We usually have three kinds of generic-reference constructions. Let me quote from an expert on this topic, John Lawler:

Definite Generic: the + Singular Noun
The tiger is in danger of becoming extinct.

Plural Generic: 0 + Plural Noun [0 = Zero Article]
Tigers are in danger of becoming extinct.

Indefinite Generic: a + Singular Noun
A madrigal is polyphonic.

The word Man in its noncount sense is often capitalized and its meaning is very much similar to the meaning of the tiger in "The tiger is in danger of becoming extinct". So Man, when used this way, could be called a "definite generic noun phrase".

"Man is not smart" is a valid generic noun phrase. You cannot use are in place of is, because Man remains grammatically singular even while being noncount.

Why Then We Usually Don't Say 'I Am Man'?

I did a search and I managed to find these examples:

While Shakespeare's tragic tale is focused upon Otello and his wife, Desdemona, it is driven by the evil force of the Darth Vader-like character, Iago. "I am evil because I am man, what evil I do is decreed by fate." (Enquirer, 2004)

And this:

What will become of this? As I am man,
My state is desperate for my master's love;
As I am woman,—now alas the day!—
What thriftless sighs shall poor Olivia breathe!
(Shakespeare, Twelth Night)

But such examples are rare, and could be explained by the use of "poetic license". In poetry, we sometimes omit articles.

Why are these examples untypical? Because here the role of man is not that of a generic noun phrase. Here, man is used to "describe" another thing - a pronoun (I).

"I am man" is an example of a copular construction. We have the subject (I), the copular verb be, and the subject complement man. The subject complement "describes" the subject. Examples of copular constructions:

Paganini was a great violinist. (copular verb "was", then a noun phrase that describes Paganini. "Who was he? - He was a great violinist)
Dostoyevsky was a Russian writer.

For such "descriptive roles" we usually use the indefinite article (a). This happens in copular constructions, and in some other "descriptive" constructions:

My daughter is training as a radiologist.
We found Lisbon (to be) a delightful city.

That's why the sentence "I am man" is highly untypical. Being a descriptive copular construction, it invites the use of a.

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P.S. Note that you can say:

I am man enough to face this challenge.

But in this sentence, the word man is used adjectively. "I am sufficiently manly to face this challenge". We can sometimes use nouns in "adjective roles".

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P.P.S. I failed to point out that "I am man" could also mean "I am the human race" - kudos to Jay.

Answer 2

When we say that word can be countable or uncountable, that doesn't mean that the two are interchangeable, and that including an article or a number is simply optional. They mean different things.

"Man" as a countable noun means a male human being, or, depending on context, an individual human being of either sex. "Man" as an uncountable noun means the human race as a whole.

"Bob is a man." Bob is a male human being.

"A man should think before he acts." A human being should think before he or she acts. "Man" here is probably intended to include both males and females.

"Man's written history goes back thousands of years." The human race has written history, etc.

"I am a man" means that I am a male human being. It's common for a person to say or write this when he wants to say that he is male and not female. (Usually in a context where the other person cannot tell by looking at you, for example, in an email.) Or someone might say, "No, no, Fred isn't my dog; Fred is a man", that is, he is a human being, not some other creature.

"I am man" literally means "I am the human race", which presumably can't be literally true. You might say this in a poetic sense -- not necessarily just in a poem, but when writing poetically -- to mean that you represent the human race in some way, or that you are speaking as the personification of the human race. Like, "I am man. I stand alone against the forces of nature. For thousands of years I have lived upon the Earth ..." or something of that sort.

Note this is not unique to the word "man". For example, "light" can be an uncountable noun, meaning the opposite of darkness or the form of energy; or it can be a countable noun, referring to a particular source of light, such as a lamp. Like "man", the two are not interchangeable. You can point to a particular lamp and say, "Here is a light", but you cannot point to a lamp and say, "Here is light" in a literal sense. You can say, "It is better to live in light than in darkness", but not "It is better to live in a light ...", unless you mean that you have a very large lamp and you are living inside it. (A lighthouse, maybe?) Etc.