From this list of tags:

SBAR - Clause introduced by a (possibly empty) subordinating conjunction.

This site explains what a subordinating conjunction is. But how can you have an empty subordinating conjunction? What are examples of sentences that should be SBAR not just S?

2 Answers 2


I think you might be being thrown by "clause", which need not mean "sentence". Consider the following pair of sentences.

(1) [S I can't believe [SBAR that John went without me.]]

(2) [S I can't believe [SBAR __ John went without me.]]

In both cases we have a sentence that contains a main and a subordinate clause. In (2), the subordinating conjunction (which goes by several other names as well, e.g. "complementizer") is "empty" (for various, theory-dependent definitions of empty).

  • Why don't they just call it a CP and be done with it? Nov 19, 2014 at 0:59
  • The S and SBAR notation pre-dates the CP/IP/TP/etc phrasal node labels of recent/current incarnations of generative syntax. Also, I believe, although I hope someone will correct me if I'm wrong, that the computational linguists who first put together the Treebank & tagset (Marcus et al. 1992, I think?) weren't particularly inclined toward the theoretical direction of later-GB, and opted for a slightly more theory-neutral approach (although I suppose that's up for debate).
    – Fred
    Nov 19, 2014 at 1:22

This link Might Help you: Penn TreeBank II Tags.
PS: As I don't have enough reputation to add this link as a comment, so I am posting link as a answer.

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