 So if we require full (unrestricted) additivity, rather than merely countable additivity, then we can see that at most countably many events have positive probability, and their probabilities sum to 1. A probability distribution with these features, where events of probability 0 have been removed, is known as a discrete distribution (such as the Poisson, geometric, or negative binomial distributions). For such a distribution, the probabilities of the individual states determine the probabilities of all events through the use of additivity.