||I DON'T KNOW . . . YET 17 absence of total knowledge. Our strong genetic and cultural past, and our homeostatic mechanisms comfort us and assure our future. That future lies with our history, as surely biologically as it does culturally. As health professionals, we render ourselves able to exercise our expertise only if we are able to say comfortably and often and with courage, "I don't know." Then add, with scientific and spiritual optimism, "Yet." Such optimistic modesty will spotlight opportunities for growth. It expresses concern and commitment to those who depend on us for professional advice. And, with an acceptance of the tentativeness of most answers, including our own, we promote tolerance for others and their points of view at a time in this country when there appears to be a rising intolerance for opposing opinion. In our universities we will continue to pursue full understanding, both of the forces which bear on us from without and from within. But in the absence of all knowledge and even in the absence of questions yet to be formed, an argument can be made for the value of tentativeness, modesty, and yet willingness to take action in the absence of full knowledge. There is a line added by theatre to Dickens', Tale of Two Cities, at the moment when the poor, innocent, and confused seamstress was riding to the guillotine with Sydney Carton. Carton brought her comfort and perhaps insight with his last whisper, "Now is not a time for understanding, now is a time for courage." Restated for our purposes, courage is required while we seek understanding. The courage for us to live out our days and challenge our nights. The courage to continue to insist on proof. And the courage to say, "I don't know . . . yet."