The definitions of "negative knowledge" and the studies in this regard published to date have not considered the categorial distinction Wittgenstein established between knowledge and certainty. Hence, the important role that certainty, despite its omission, should have in these definitions and studies has not yet been shown. In this article, I contrast the term "negative certainty" with that of "negative knowledge" in order to clarify this concept by describing its significant differences with the first. To characterize negative certainty, I base upon two criteria: on the one hand, negative certainty cannot be directly excluded by a positive certainty, and on the other hand, negative certainty must have an obvious and practical usefulness in which its negative nature is clearly appreciated. To illustrate the use of these two criteria, I describe four examples of negative certainty, paying special attention to their educational implications as well as the contrast between negative certainty and negative knowledge.