Profound books are always worthwhile. If we agree with them, their ideas become a direct contribution to our knowledge. If we disagree, they impel us to examine the basis of disagreement and to develop our own counter-ideas, and thus they make an indirect contribution to our knowledge. R. G. Collingwood's The Idea of History (Oxford, Clarendon Press, 1946) is the most penetrating work on the foundations of historical method known to me, but I find it unacceptable. My major difficulties result from his ontological idealism and his dichotomy between mind and nature.