ACTA PHILOSOPHICA FENNICA Editor: ACTA PHILOSOPHICA FENNICA Vol. 84 Ilkka Niiniluoto Editorial Board: Timo Airaksinen Leila Haaparanta Olli Koistinen Simo Knuuttila Ingmar Pörn Gabriel Sandu Acta Philosophica Fennica is published by the Philosophical Society of Finland. Since the inception ofthe series in 1935 it has been the forum for much ofthe best phiiosophical work in Finland. In 1968—1981 it was distributed by the North Holland Publishing Company (Amsterdam), and since 1981 by the Academic Book store (Helsinki). Information for Authors The Acta series publishes shorter and longer monographs as welI as coHections of articles in ali parts ofphilosophy. Authors should send their contributions to Acta PhilTosophica Fennica, Department of Philosophy, P.O. Box 9 (Siltavuorenpenger 20 A), 00014 University of Helsinki, Finland. Ali philosophical traditions and ali types of philosophy fali within the intended scope of the Acta Philosophica Fennica. It foilows from its traditional character, however, that special consideration is given to the work ofFinnish phiiosophers and to papers and monographs inspired by their contributions to philosophy, Subscription Information Permanent subscriptions can be placed directly with Bookstore Tiedekirja, Kirkko- katu 14, 00170 Helsinki, Finland, Fax +358—9—635 017. Other orders can be placed with Bookstore Tiedekirja or with The Academic Bookstore, P0. Box 128 (Keskus- katu 1), 00101 Helsinki, Finland, Fax +358—9—121 4441. PROBLEMS FROM ARMSTRONG Edited by TIM DE MEY and MARKKU KEINÄNEN HELSINKI 2008