"None but the brave deserves the fair." What part of speech is "but"?

In the sentence:

None but the brave deserves the fair.

...is the word but here a:

1. pronoun
2. adverb
3. preposition
4. conjunction

Normally but is used as conjunction, but here I am not sure if this "but" is used as a conjunction or not. Can anyone please help me?

In the sentence:

None but the brave deserves the fair.

...is the word but here a:

1. pronoun
2. adverb
3. preposition
4. conjunction

1: Pronoun

But is never a pronoun.

2: Adverb

But, the adverb, means something similar to only. If you take the word out completely the sentence will always be perfectly formed. Consider the following:

• You can but try.
• You can only try.
• You can try.

or ...

• Life is but a dream.
• Life is only a dream
• Life is a dream.

or ...

• He is but a beginner
• He is only a beginner.
• He is a beginner.

or ...

• We have but three days left.
• We have only three days left.
• We have three days left.

Notice that if the sentence with but is true, the sentence without but will also be true. The adverb but does not change the truth conditions for a sentence.

3: Preposition

But the preposition means apart from. We often see it heading a preposition phrase used as a postmodifier in a noun phrase:

• all [but one]
• everyone [but James]
• nothing [but an excuse]

Notice that this but phrase does indeed change the absolute meaning of the sentence. The following sentences do not mean the same thing at all. Their truth conditions are completely different:

• Everyone was captured.
• Everyone but James was captured.

We can normally substitute the preposition but with apart from:

• Everyone apart from James was captured.

A quite useful test is to see if including will give the opposite meaning:

• Everyone but James was captured.
• Everyone including James was captured.

In the sentences above, the fact that the preposition including gives the opposite meaning tells us that it is probably the preposition. Note that this test doesn't work if the word following but is a number:

• All including one ... (doesn't work because of the numeral)

Notice that when we have but as a preposition, it does not change the Head of the noun phrase. In the noun phrase no one but Bob, the Head of the phrase is no one. The phrase but Bob is modifying our understanding of no one.

4: Conjunction

The conjunction (or co-ordinator) but is the most common but that we see. It can always be substituted with the conjunction and and the sentence will still be truthful. Consider:

• I hit Bill but not Bob.
• I hit Bill and not Bob.

or ...

• My elephant is small but strong.
• My elephant is small and strong.

The Original Poster's sentence

None but the brave deserves the fair.

Let's try some tests. Can we substitute it with only, apart from or and:

• None only the brave deserves the fair.
• None apart from the brave deserves the fair.
• None and the brave deserves the fair.

The last sentence is not good. The meaning is different. In fact it seems to be contradictory. More importantly, the grammar is bad. We would expect a plural verb here, if we could make sense of the Subject in the first place. This cannot be the conjunction.

Now, the first sentence seems kind of marginally acceptable. The second is definitely ok. This means that it could still be but the adverb or but the preposition. Let's see if we can remove the word but. If it is the adverb, the sentence should be grammatical, and have the same truth conditions:

• *None the brave deserves the fair.

This shows that this is definitely not the adverb but. The sentence is completely ungrammatical. It is so ungrammatical we cannot know what it means. If it was but the adverb, the sentence would still make perfect sense.

It seems it must be but the preposition. Let's see whether taking out the but phrase changes the meaning. It should do:

• None but the brave deserves the fair.
• None deserves the fair.

Yes the meaning has changed here. Lastly if we use including instead of but does it give the opposite meaning:

• None, including the brave, deserves the fair.

Yes, this worked too. This is definitely but the preposition.