1. A method for creating a hierarchy of topics, the method comprising: training a topic classifier using training data, the training data comprising a plurality of trained topic pairs, each topic in the plurality of trained topic pairs selected from a predetermined list of topics; determining for each particular topic pair in a target set of topic pairs, using the topic classifier, a probability that the first topic in each particular topic pair is a parent of the second topic in each particular topic pair, the first and second topics included in the predetermined list of topics; collecting, in response to the determining the probability for each particular topic pair, a collection of probabilities for the target set of topic pairs; constructing a hierarchy of topics based upon the collection of probabilities for the target set of topic pairs.