In "US Sign and Safety" I came across the road sign shown in the image below.

Can someone explain what part of speech the word "before" is?

I'm asking because it seems that these two graphs are both valid, so "before" can be a sub- conjunction (temporal connotation) or a preposition (spatial connotation).

enter image description here

enter image description here

  • I'm not sure why this question is voted down, but, I note, especially to benefit of down-voters, that 'before', here, could be a preposition indicating where the bridge ices. This is a real problem if the driver is not a native speaker.
    – user19148
    Jul 10, 2012 at 13:42
  • 4
    Agreed, 'before' can relate to time or space, giving rise to possible confusion. It is not just a question of being a native speaker. As a British native speaker, I did not understand the sign until I read the explanation by bonomo, thinking at first that it carried the spatial meaning. Jul 10, 2012 at 15:23
  • @BarryBrown: Thank you Barry. I'm afraid that other people (the downvoters) didn't exactly understand the problem. So, I have improved my question with a graph to better explain what I asked.
    – user19148
    Jul 10, 2012 at 15:31

3 Answers 3


Easy. One tree is deeper structure than the other, so they're both valid, but at different stages of the derivation.

The one on the right, with the complete transitive clause, is what it means, pretty clearly; that's a "deep structure". The one on the left, after the verb is deleted by Conjunction Reduction, is a "surface structure". The terms refer to the meaning and fully-marked structure of an utterance as being "deep", and the syntax that actually occurs after syntactic changes as being on "the surface", part of A Mind is A Container metaphor theme (and since thought is fluid, this comes out as A Pool).

The issue is apparently how the tree node over before should be labelled. That's of no particular consequence; it's the same structure either way. Since it is inconsequential, however, linguists argue about it constantly, though they'd all agree:

  • it's a node in the tree
  • it's a node in that place in the tree
  • it's a node that governs before

The important things are the things that they would agree on. Many syntactic phenomena change the grammatical class of words; There-insertion makes a Subject (and therefore a Noun Phrase) out of there, for instance, which is at least surprising. Temporal and locative prepositions, conjunctions, and adverbs (and phrasal verb "particles") like up change their role to suit their usage in a construction.

So how you label that node is up to you. This is one big reason why I keep saying that asking what Part Of Speech a given word is tells you nothing at all about that word; only about the particular construction with the word. It's constructions that are important.


From here

The Bridge Ices Before Road sign warns drivers that the bridge is more likely to have ice form on it before it occurs on the road. This happens because cold air is able to surround the upper and lower surface of the bridge. This double exposure to freezing air causes the water on the bridge to freeze faster than that on the road. The water on the road is kept from freezing longer because the ground is usually warmer than the air and thus able to prevent its freezing for a long period of time.

  • Should be: "This double exposure to freezing air..." No copy editor for that web page, I guess.
    – JLG
    Jul 10, 2012 at 15:00
  • 4
    This sign is rather common where I live, at least during the months between November and March. Essentially, it is a caution, a warning: Just because the road you've been driving on isn't slick with ice, doesn't mean the bridge you're about to cross isn't slick with ice.
    – J.R.
    Jul 10, 2012 at 16:13

Of course the intention is along the lines of: "Be aware of that fact that, as temperatures drop under freezing, the part of the road over a bridge will develop ice before the rest of the road will."

You can't fit all that on a sign though. Street signs are famous for economizing space by throwing out articles and punctuation that might normally be required to avoid ambiguity. Most folks are sharp enough to work out which meaning was intended from context.

There are numerous examples of this. My personal favorite is:

enter image description here

Obviously the intent is not that the people who put up the sign are telling you that their children are slow. Still, it's fun to pretend that's what they mean. :-)

  • 3
    Or else that you should slow (down) children who are running...
    – Paola
    Jul 10, 2012 at 17:25
  • 4
    Side note, judging by the musculature of the figure on the sign, that is not a child; maybe a tiny bodybuilder.
    – Andy
    Jul 10, 2012 at 17:37

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