You can either say : كانوا لطيفين or كانوا لطفاء Lotafa' but لطيفون would be wrong here. As you know, in Arabic a word can have several plurals One common form of plural is the "sound masculine plural" جمع المذكر السالم Which is formed by adding ون or ين to a masculine adjective Whether you use ليطفون or لطيفين depends on the word position in the phrase. For example If it comes as a subject مبتدأ or predicate or خبر you use لطيفون . where as if it comes as an object or after a preposition or in the example you mentioned it would be لطيفين Check this pdf file : http://quranicarabic.files.wordpress.com/2010/02/15-lesson-13-the-masculine-plural6.pdf it's about the "sound masculine plural". Starting from page 180 but this is a bit advanced and actually many Arabs get confused about when to use ون and ين You can also use لطفاء which is the more common plural for لطيف You may also find this blog useful :) http://quranicarabic.wordpress.com/quraanic-arabic/