Two studies were conducted to examine children's understanding of three terms that denote different degrees of likelihood: possibly, probably and definitely. In Study 1, children in preschool, and first, third and fourth grade completed a comparison task involving pairs of likelihood terms. Twelve stories were created that described the likelihood that each of two children would participate in an activity, and subjects judged which of the two children actually participated. In Study 2, children in preschool, and first, third and fifth grade evaluated separate statements describing three different children, each of whom was said to have a different estimate of the likelihood that a scary event depicted in a movie would actually occur. Subjects rated how scared each of the three children felt. The results of the two studies revealed that preschoolers showed very little comprehension of the meaning of any of the three words, but by fourth grade the majority of children distinguished among all three terms. Children understood the distinction between definitely and both of the other terms (possibly, probably) better than they understood the distinction between possibly and probably. This finding is consistent with research on the development of children's understanding of probability concepts. Unexpectedly, the distinction between probably and definitely seems to emerge at a younger age than the distinction between possibly and definitely. The findings are discussed in terms of their implications for communicating verbal messages to children.