As any well educated GGer knows, there is a big and important difference between grammaticality and acceptability (see here and here) (don’t be confused by the incessant attempts by many (especially psycho types) to confuse these very separate notions (some still call judgment tasks ‘grammaticality judgments’ (sheesh!!))). The latter pertains to native speaker intuitions, the former to GGers theoretical proposals. It is a surprising and very useful fact that native speaker’s have relatively stable converging judgments about the acceptability (under an interpretation) of linguistic forms over a pretty wide domain of linguistic stimuli. This need not have been the case, but it is. Moreover, this capacity to discriminate among different linguistic examples and to comparatively rate them consistently over a large domain has proven to be a very good probe into the (invisible underlying) G structure that GGers have postulated is involved in linguistic competence. So for lots of GG research (the bulk of it I would estimate) the road to grammaticality has been paved by acceptability. As I’ve mentioned before (and will do so again here), we should be quite surprised that a crude question like “how does this sound (with this meaning)?” has been able to yield so much. IMO, it strongly suggests that FL is a (relatively) modular system (and hence immune to standard kinds of interference effects) and FL is a central cognitive component of human mental life (which is why its outputs have robust behavioral effects). At any rate, acceptability’s nice properties makes life relatively easy for GGers like me as it allow me/us to wallow in experimental crudity without paying too high an empirical price.
That is the good news. Now for some bad. The fact that acceptability judgments are fast and easy does not mean that they can be treated cavalierly. Not all acceptability judgments are equally useful. The good ones control for the non-grammatical factors that we all know affect acceptability. The good ones general exploit minimal pairs to control for these distorting non-grammatical factors. Sadly, one problem with lots of work in syntax is its lack of fastidiousness concerning minimal pairs. Let’s consider for a moment why this is a problem.
If acceptability is our main empirical probe into grammaticality and it is understood that acceptability is multivariate with grammaticality being but one factor among many contributing to acceptability, then to isolate what the grammar contributes to an acceptability judgment requires controlling for all acceptability effects that are not grammatically induced. So, the key factor behind the acceptability judgment methodology is to bend over backwards to segregate those factors that we all know can affect acceptability but cannot be traced to grammaticality. And it is the practicing GGer that needs to worry about the controls because speakers cannot be trusted to do so as they have no special conscious insight into their grammatical knowledge (they cannot tell us reliably why something sounds unacceptable and whether that is because their G treats it as ungrammatical). And that is where minimal pairs come in. They efficiently function to control for non-grammatical factors like length, lexical frequency, pragmatic appropriateness, semantic coherence, etc. Or, to put this another way: to the degree that I can use largely the same lexical items, in largely the same order to that degree I can control for features other than structural difference and thereby focus on G distinctions as the source for whatever acceptability differences I observe. This is what good minimal pairs do and so this is what makes minimal pairs the required currency of grammatical commerce. Thus, when they are absent suspicion is warranted, and best practice would encourage their constant use. In what follows I would like to illustrate what I have in mind by considering a relatively hot issue nowadays; the grammatical status of Island Effects (IE) and how minimal pairs correctly deployed, render a lot of the argument against the grammatical nature of island effects largely irrelevant. I will return to this theme at the end.
To get started, let’s consider an early example from Chomsky (1964: Current Issues). He observes that (1) is three ways ambiguous. It has the three paraphrases in (2).
1. John watched a woman walking to Grand Central Station (GCS)
2. a. John watched a woman while he was walking to GCS
b. John watched a woman that was walking to GCS
c. John watched a woman walk to GCS
The ambiguities reflect structural differences that the same sequence of words can have. In (2a), walking to GCS is a gerundive adjunct and John is the controller of the subject PRO. In (2b) a woman walking to GCS is a reduced relative clause with walking to GCS an adjunct modifying the head woman. In contrast to the first reading, a woman walking to GCS forms a nominal constituent. In the third reading a woman walking to GCS is a gerundive clausal complement of watch depicting an event. It is thematically similar to, but aspectually different from, the naked infinitive small clause provided in (2c). Thus, the three way ambiguity witnessed in (1) is the product of three different syntactic configurations that this string of words can realize and that is made evident in the paraphrases in (2).
Chomsky further notes that if we WH move the object of to (optionally pied piping the preposition) all but the third reading disappears:
3. a. Which train station did John watch a woman walking to
b. To which train station did John watch a woman walking
Given what we know about islands and movement, this should not be surprising. Temporal adjuncts resist WH extraction (CED effects), as do relative clauses (CNPC). Clausal complements do not. Thus, we predict that movement of (to)which train station from (1) with structures analogous to (2a,b) should be illicit, while movement from (1) with a complement structure like (2c) should be fine. Thus, we expect the movement to factor out all but one of the readings we find with (1). And this is what occurs.
Note that this explanation of the loss of all but one reading coincides with the fact that all but the third paraphrase in (2) resists WH extraction:
4. a. *(To) which train station did John watch a woman while he was walking (to)
b. *(To) which train station did John watch a woman who was walking (to)
c. (To) which train station did John watch a woman walk (to)
Thus the reason that (3) becomes monoguous under WH movement is the same reason that (4a,b) are far more unacceptable than (4c). This argues for the fact that unacceptability wrt these sentences ((un)acceptability under an interpretation for (1) and tout court with (4)) implicates a syntactic source precisely because other plausible factors are controlled for, and they are controlled for because we have used the same words, in the same order thereby varying only the grammatical structures that they realize.
We can go a little further, IMO. Note the dependent measure in (4) is relative acceptability with (4c) as baseline. But, note that in this case the items compared are not identical. The fact that we get the same effects in (1)/(3) as we do in (2)/(4) argues that the data in (4) reflects structural differences and not the extraneous vocabulary items that differ among the examples. Furthermore, the absence of the two illicit readings in (3) is quite clear. It is often asserted that acceptability judgments are murky and can be trivially enhanced/degraded by changing the WHs moved or the intervening lexical items. Perhaps. Here we have a case where the facts strike me as particularly clear. Only the event reading survives the extraction. The other ones disappear, which is exactly what a standard theory of islands would predict. This, I believe, is typical for well constructed minimal pair cases: the dependent measure will often be the availability of a reading and, interestingly, the presence/absence of a reading is often more perspicuous for native speakers than is a more direct relatively acceptability judgment.
I would like to consider one more case for illustration. This involves near minimal pairs rather than identical strings. What the above Chomsky case provides evidence for (rather clear evidence IMO) is that G structure matters for extraction. It shows this by factoring out everything but such structure as the relevant variable. However, it does not factor out one important variable: meaning. Sentence (1) has three readings in virtue of having three different syntactic structures. So, the argument cannot single out whether the relevant factor is syntactic or semantic. Does the difference under WH movement reflect the effects of formal grammatical structure (syntax) or of meaning (semantics)? As the two vary together in these cases, it is impossible to pull them apart. What we need to focus in on this are structures that are semantically and formally the same. And this is very hard to do. However, not quite impossible. Let me discuss a (near) minimal pair involving event complements.
Consider the following two sets of sentences:
5. a. Mary heard the sneaky burglar clumsily attempt to open the door
b. Mary heard the sneaky burglar’s clumsy attempt to open the door
c. What1 did Mary hear the sneaky burglar clumsily attempt to open t1
d. What1 did Mary hear the sneaky burglar’s clumsy attempt to open t1
6. a. Mary heard someone clumsily attempt to open the door
b. Mary heard a clumsy attempt to open the door
c. What1 did Mary hear someone clumsily attempt to open t1
d. What1 did Mary hear a clumsy attempt to open t1
The main difference between (5) and (6) is that the latter tries to control for definiteness effects in nominals. What is relevant here is that both sets of cases distinguish the acceptability of the the c from the d cases with the former being judged better than the latter using standard Sprouse like techniques (i.e. we find a super additivity effect for (5c)/(6c)). Why is this interesting?
Well note that the near minimal pairs have a common semantics. Perception verbs take eventive internal arguments. These can come in either a clausal ((5a,c)/(6a,c)) or a nominal ((5b,d)/(6b,d)) flavor. The latter should show island effects under movement given standard subjacency reasoning. In sum, these examples control for semantic effects by identifying them across the two syntactic structures yet we still find the super-additivity signature characteristic of islands. This argues for a syntactic (rather than a semantic) conception of islands for this is the one factor we varied in these near minimal pairs, the meaning having been held constant across the a/b and c/d examples.
Howard Lasnik is constantly reminding those around him how important minimal pairs are in constructing a decent grammatical argument. He notes this because it is not yet second nature for GGers to employ them. And he is right to insist that we do so for the reasons outlined above. It allows us to make our arguments cleaner and to control for plausible interfering factors. Minimal pairs is the nod we give to the fact that acceptability judgments are little experiments with all the confounds that experiments bring with them. Minimal pairs is the price we pay for using acceptability judgments to probe grammatical structure. As Chomsky noted long ago in Syntactic Structures these sorts of judgments can really get you deep into a G structure very efficiently. They are an indispensible part of linguistic theorizing. However, to do their job well, we must understand their logic. We must understand that theories of grammar are not theories of acceptability and that there is a gap between acceptability (a term of art for describing data) and grammaticality (a term of art for describing the products of generative procedures). Happily the gap can be bridged and acceptability can be fruitfully used. But jumping that gap means controlling for extraneous factors that impact acceptability. And that is how minimal pairs are critical. Deployed well they allow us to control the hell out of the data and zero in the grammatical factors of linguistic interest. So, let’s hear it for minimal pairs and let’s all promise to use them in all of our papers and presentation from now on. Pledges to do so can be sent to me written on a five dollar bill c/o the ling dept at UMD.
 Jon Sprouse and friends have shown roughly this: that crude methods are fine as they converge with more careful ones.
 If undergrads are to be believed virtually all unacceptability stems from semantic ill-formedness. If asked why some form sounds off you can bet dollars to doughnuts that an undergrad will insist that it doesn’t mean anything, even when telling you what it in fact means.
 Which, you all know, does not exist but is actually a copy/occurrence of John due to sidewards internal merge. And yes, this is an unpaid political announcement.
 Note the use of ‘grammatical’ rather than ‘syntactic.’ These cases implicate structure but as syntactic structure and semantic interpretation co-vary we cannot isolate one or the other as the relevant causal element. We return to this with the second example of a minimal pair below.