1. A method of operating a computing device, the method comprising: receiving a speech input comprising an indefinite quantitative term; determining a mapping of the indefinite quantitative term to a first definite quantity; applying the first definite quantity to an action performed via the computing device in response to the speech input; receiving a follow-up speech input that requests performance of an additional quantity of the action performed; and modifying the mapping of the indefinite quantitative term to a second definite quantity based upon the follow-up speech input.