That dream action and so-called real action could be indistinguishable might seem to be a criticism of Wittgenstein’s notion of certainty. What kind of notion is this? Isn’t a dream action secondary to real action? If the two are put on the same plane, is something lost?
Such a criticism fails to distinguish between certainty and knowledge. Knowledge, which will be dealt with in more detail, is public—it depends on other people, a consensus view, as it were. Certainty, though, is a personal affair. As Wittgenstein says, “Knowledge is in the end based on acknowledgment” (328). This dictum helps to distinguish between knowledge and certainty. One would never acknowledge (in the usual usage of the word) that he’s certain of something. There are situations that may call for one’s saying, “I am certain of…”; but this usage is not the same as saying, “I know…”; the latter is an acknowledgement of a piece of discourse, a so-called truth. Such an acknowledgement takes place in a public sphere. To make sense of this distinction, think of something that only you could be said to know, your favorite color for instance. To say that you know your favorite color is to go only as far as saying that you have a favorite color. Saying you know your favorite color could be called for by a situation, someone doubting whether you have a favorite color, maybe. But it’s a piece of unnecessary verbiage to say, “I know my favorite color; it’s orange.” It is not so unnecessary to say, though, “I know the capital of the U.S.; it’s Washington”. The reason for this distinction is that knowledge hinges upon the ability for a state of affairs to be or not be the case; that is, for the negation of a knowledge proposition to make sense. To say, “I don’t know my favorite color” (assuming, though, that you have one) would be a piece of nonsense. To say, “I don’t know the capital of the U.S.” merely shows an ignorance. This asymmetry between knowledge and certainty hinges on the public nature of knowledge versus the private nature of non-knowledge propositions of the type dealing with favorite colors, pain or fear. Such a private proposition should not be regarded as part of a language, which is shared by people; nor should it be regarded as a piece of knowledge, for it’s impossible for one to be wrong about such a proposition. Something about which it’s impossible to be wrong underlies our entire system of knowing and speaking.