I'm studying syntax with 'Introduction to government and binding theory' by Haegeman by myself and I encountered something I don't understand.

According to PRO theorem, PRO must be ungoverned. And these two sentences were presented.

(a) *John doesn't know [if [PRO to leave]].
(b) John doesn't know [whether [PRO to leave]].

And he explains that in (a), if is the head and it governs PRO so the sentence is ungrammatical. But in (b), whether is at the [Spec, CP] position so nothing governs PRO and the sentence is grammatical.

As I understood earlier, if and whether are samely complementizer. But how come if goes in [C, CP] while whether goes in [Spec, CP]? Why these two act differently and how can I tell it?

I'd appreciate it if someone could help me. Thanks! (If I posted this on the wrong place, please let me know. I'm not sure if I should go to English forum.)

  • 1
    Since non-terminal nodes never appear in the data, you can put whatever words you like in them. In this case, arranging things the suggested way makes this difference (whether can govern an infinitive VP, but if can't) seem to fall out naturally, instead of being a random chunk of difference between two lexemes.
    – jlawler
    Jul 12, 2017 at 17:34
  • 2
    The query pro-forms have more functions than simple subordination. 'Whether' is a query pro-form for 'either', with the other choice (to stay) elided in your example.
    – amI
    Jul 12, 2017 at 21:42
  • In (b) "whether" is an interrogative subordinator introducing an interrogative infinitival. The meaning is deontic, as if the modal "should" were included: John doesn't know whether he should leave. By contrast, the subordinator "if" cannot introduce interrogative infinitives -- only subordinate content clauses (embedded questions) which (a) is not. Which explains why it is ungrammatical.
    – BillJ
    Jul 15, 2017 at 16:07

1 Answer 1


In spite of what elementary textbooks tend to say, i.e., that the values of Comp are that (or 'null that'), whether, if and for (or 'null' for) in English, there is well established syntactic evidence that that initial analysis - dating back to the late 60's and early 70's - was incorrect.

As a matter of fact, whether is, like when, why, where, how much, what book, under what conditions, etc., a wh-phrase landing in Spec Focus, not a Comp head.

The simplest argument in this respect is that whether can be coordinated with other wh-phrases that must themselves occupy Spec Focus, whereas if cannot. Thus, in I would like to know whether and (,if so,) under what conditions I could postpone payment of my teaching fees, whether is clearly coordinated with a PP phrase and both land first in Spec Focus and then in Spec C (not in Focus and C!). Or, to take a different example, whether can also be coordinated with not, as in I would like to know whether or not I am admitted to the AI programme, where not is independently known to be a phrase base-generated in Spec Polarity (but not in the head of Polarity, as initially assumed). On the contrary, if, a C head, cannot be so coordinated, cf. * I would like to know if or not I am admitted to the AI programme.

Confirming evidence is available if you consider the etymology of whether (from OE hw-aeither) - or, for that matter, that of not (from n(e)+a+wiht, approximately 'not a bit', a negative noun phrase). Significantly, in Old and Middle English, hwaether did not interfere with the ascension of the finite verb into the head of FocusP. Although it is true that the finite verb did not have to ascend in hwaether-introduced clauses, and did not usually do (as in Modern English), the OED still cites quite a few OE and ME examples in which it does, yielding the word order ...hwaether + Verb + Subject...).

Of course, if hwaether had been a C (or Focus) head, such verb-raising would not have been possible in any case, because the finite verb is itself a head and can raise only into an empty head position (= Head Movement). Consequently, hwaether was already a specifier, as it is today, in Old and Middle English.

  • Thank you! It's weird that this book explains that the values of Comp are that, if, whether, for (as you mentioned) and says nothing about that whether is a type of wh-phrase. It helped me a lot anyway! Jul 14, 2017 at 15:00
  • 1
    You are right, especially because the idea that 'whether' is just another interrogative WH-element and that 'yes/no [= polarity] questions are just a particular case of 'wh-questions' dates back to Katz & Postal's 'An Integrated Theory of Linguistic descriptions' (MIT, 1964) (see chapter 4, pp. 95-97 and ff., in particular). What disguises this fact is that 'whether' (< wh+either-yes or not) questions the value of the POLARITY of the clause, a sentence adverbial, which is phonetically null when positive (= unmarked), although visible as the Polarity specifier 'not' when negative (= marked).
    – user6814
    Jul 16, 2017 at 8:55

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