 It seems wrong to say that The Turing Test is defective because it is a “null effect experiment”. True enough, there is a sense in which The Turing Test does look for a “null result”: if ordinary judges in the specified circumstances fail to identify the machine (at a given level of success), then there is a given likelihood that the machine is intelligent. But the point of insisting on “ordinary judges” in the specified circumstances is precisely to rule out irrelevant ways of identifying the machine (i.e. ways of identifying the machine that are not relevant to the question whether it is intelligent). There might be all kinds of irrelevant differences between a given kind of machine and a human being—not all of them rendered undetectable by the experimental set-up that Turing describes—but The Turing Test will remain a good test provided that it is able to ignore these irrelevant differences.