 In his teaching career at Denver Seminary, he has taught graduate courses in Christian Apologetics, Problems in Apologetics, Issues in Philosophy of Religion, Christian Ethics and Modern Culture, and Religious Pluralism, among many others.He is a member of the Society of Christian Philosophers and the Evangelical Philosophical Society, has published twelve books and contributed to many others, and has written numerous articles, book reviews, and editorials.Articles have appeared in periodicals such as "Christianity Today", the "Journal of the Evangelical Theological Society", "Philosophia Christi", and "Moody Monthly".