Analogy is a powerful comparison mechanism, commonly thought to be central to human problem solving. Analogies like "an atom is like the solar system" enable people to effectively transfer knowledge to new domains. Can we enable computers to do similar comparisons? Prior work on analogy (structure mapping) provides guidance about the nature of analogies, but implementations of these theories are inefficient and brittle. We are working on a new analogy mechanism that uses instance learning to make robust, efficient comparisons.