These words refer to the ease with which, or likelihood that, something can be done. Viable means "capable of living," "physically fitted to live," but by extension has come to mean "able or likely to produce continued success or effectiveness" and is often used in a comparative sense: "Your plan is more viable than the one we have been using." Workable is applied to plans, suggestions, or ideas that will be successful if properly managed: "The foreman presented us with a workable production schedule." Words closely related to these near-synonyms are feasible, practical, and possible.
Dictionary of problem words and expressions. Harry Shaw. 1975.