Austin analyzed the ordinary meaning of "I can," and argued that there might be an implicit "if" lurking in the background of such statements. "Are cans constitutionally iffy?," he asked in his famous 1956 essay "Ifs and Cans."

In his Ethics, G. E. Moore had made free will compatible with determinism by analyzing the phrase "could have done otherwise" as meaning, "could have done otherwise, if I had chosen to do otherwise"

Austin then asks, could I have done otherwise? Could I have made the putt, in exactly the same physical conditions? "Further experiments," he says, "may confirm my belief that I could have done it although I did not." This is a sound empirical point of view. If Austin tries to hole the putt several times - on the same green, the same "lie" of the ball, the same distance to the hole, etc. - and finds that he does succeed, say, 95% of the time, it is reasonable to say that he could have, indeed normally would have, holed the putt. Physical reality often gives us only a statistical probability concerning what we "can" do.

In his work, Ethics, P.H.Nowell-Smith, who is also trying to come to grips with the implications of determinism, argues that "could have" means "would have, if." But Austin argues that this cannot be the categorical statement Nowell-Smith makes of it, because there are so many other conditionals that might be part of the "if" clause - if he had the opportunity, if he had the ability, if he was lucky, etc.

First, don't miss the irony that Dennett is using "possible worlds" thinking, which makes the one world we are in only able to have one possible future, our actual world.

Dennett says

Now that we have a clearer understanding of possible worlds, we can expose three major confusions about possibility and causation that have bedeviled the quest for an account of free will. First is the fear that determinism reduces our possibilities. We can see why the claim seems to have merit by considering a famous example proposed many years ago by John Austin:

Consider the case where I miss a very short putt and kick myself because I could have holed it. It is not that I should have holed it if I had tried: I did try, and missed. It is not that I should have holed it if conditions had been different: that might of course be so, but I am talking about conditions as they precisely were, and asserting that I could have holed it. There is the rub. Nor does "I can hole it this time" mean that I shall hole it this time if I try or if anything else; for I may try and miss, and yet not be convinced that I could not have done it; indeed, further experiments may confirm my belief that I could have done it that time, although I did not. (Austin 1961, p. 166)

Austin didn't hole the putt. Could he have, if determinism is true? The possible-worlds interpretation exposes the misstep in Austin's thinking. First, suppose that determinism holds, and that Austin misses, and let H be the sentence "Austin holes the putt." We now need to choose the set X of relevant possible worlds that we need to canvass to see whether he could have made it. Suppose X is chosen to be the set of physically possible worlds that are identical to the actual world at some time t₀ prior to the putt. Since determinism says that there is at any instant exactly one physically possible future, this set of worlds has just one member, the actual world, the world in which Austin misses. So, choosing set X in this way, we get the result that H does not hold for any world in X. So it was not possible, on this reading, for Austin to hole the putt.

To include adjacent worlds seems to add alternative possibilities?

Of course, this method of choosing X (call it the narrow method) is only one among many. Suppose we were to admit into X worlds that differ in a few imperceptibly microscopic ways from actuality at t₀; we might well find that we've now included worlds in which Austin holes the putt, even when determinism obtains. This is, after all, what recent work on chaos has shown: Many phenomena of interest to us can change radically if one minutely alters the initial conditions. So the question is: When people contend that events are possible, are they really thinking in terms of the narrow method?

Suppose that Austin is an utterly incompetent golfer, and his partner in today's foursome is inclined to deny that he could have made the putt. If we let X range too widely, we may include worlds in which Austin, thanks to years of expensive lessons, winds up a championship player who holes the putt easily. That is not what Austin is claiming, presumably. Austin seems to endorse the narrow method of choosing X when he insists that he is "talking about conditions as they precisely were." Yet in the next sentence he seems to rescind this endorsement, observing that "further experiments may confirm my belief that I could have done it that time, although I did not." What further experiments might indeed confirm Austin's belief that he could have done it? Experiments on the putting green? Would his belief be shored up by his setting up and sinking near-duplicates of that short putt ten times in a row? If this is the sort of experiment he has in mind, then he is not as interested as he claims he is in conditions as they precisely were. To see this, suppose instead that Austin's "further experiments" consisted in taking out a box of matches and lighting ten in a row. "See," he says, "I could have made that very putt." We would rightly object that his experiments had absolutely no bearing on his claim. Sinking ten short putts would have no more bearing on his claim, understood in the narrow sense as a claim about "conditions as they precisely were." We suggest that Austin would be content to consider "Austin holes the putt" possible if, in situations very similar to the actual occasion in question, he holes the putt. We think that this is what he meant, and that he would be right to think about his putt this way. This is the familiar, reasonable, useful way to conduct "further experiments" whenever we are interested in understanding the causation involved in a phenomenon of interest. We vary the initial conditions slightly (and often systematically) to see what changes and what stays the same. This is the way to gather useful information from the world to guide our further campaigns of avoidance and enhancement.

Curiously, this very point was made, at least obliquely, by G. E. Moore in the work Austin was criticizing in the passage quoted. Moore's examples were simple: Cats can climb trees and dogs can't, and a steamship that is now traveling at 25 knots can, of course, also steam at 20 knots (but not, of course, in precisely the circumstances it is now in, with the engine set at Full Speed Ahead). The sense of "can" invoked in these uncontroversial claims, the sense called "can (general)" by Honoré (1964) in an important but neglected article, is one that requires us to look not at "conditions as they precisely were" but at minor variations on those conditions.

So Austin equivocates when he discusses possibilities. In truth, the narrow method of choosing X does not have the significance that he and many others imagine. From this it follows that the truth or falsity of determinism should not affect our belief that certain unrealized events were nevertheless "possible," in an important everyday sense of the word. We can bolster this last claim by paying a visit to a narrow domain in which we know with certainty that determinism reigns: the realm of chess-playing computer programs.

(Freedom Evolves, pp. 75-77)