Define relevant cost. Why are historical costs irrelevant? A - Relevant costs are expected future costs that differ among alternative courses of action being considered. A historical cost is just predicted or forecast cost. Instructors Q A historical cost is predicted?! Criteria If answer is outside of our textbook, please provide your source or reference, if within, provide the page or pages. Reference - Horngren, C. T., Datar, S.M., Foster, G., Rajan, M., & Ittner, C. (2009). Cost Accounting: A Managerial Emphasis (13th ed.). Upper Saddle River, NJ: Pearson Prentice Hall, pp. 27 & 388