Two of Virginia Tech's most distinguished teacher/scholars -- Gary Downey, Alumni Distinguished Professor in the Department of Science and Technology in Society in the College of Liberal Arts and Human Sciences, and Marc Edwards, the Charles Lunsford Professor of Civil Engineering in the College of Engineering and 2007 John D. and Catherine MacArthur Fellow -- will deliver the keynote addresses at Virginia Tech's 2008 Fall University and Graduate School Commencement ceremonies to be held Friday, Dec. 19.