While it is trite to speak of the realism of St. Thomas, it is less so, perhaps, to attempt to give its precise shade and meaning. The initial question, which I should wish briefly to answer, is whether or not this realism is in the technical sense a critical realism. We are all aware of what is meant by the critical approach which is said, rightly or wrongly, to mark one of the great advances of modem thought. It is just this critical approach which is said to separate thought lifted to the philosophical level from thought which remains on the popular level of ordinary, and perhaps puerile, intelligence. The critical approach requires that the mind should no longer accept anything that does not completely justify itself before the mental court of enquiry. Anteriorly, common sense accepts without discussion a certain number of natural certitudes. Moreover, it is possible to conceive of a philosophy rooted in common sense, which accepts all that the latter accepts in order to hasten forward to the discovery of new truths. To delve into the mystery of things, to scale the heavens, to soar on intrepid wing up into the infinite heights of metaphysics, that is indeed worth the labour of the dialectical effort it demands.

Of what use is it to philosophize except in order to know a little more than that which everybody knows without even having learnt it? But first of all Descartes and, following him, Kant, and after them the whole of nineteenth century philosophy, come to pour cold water on this fine enthusiasm. Before leaving for the stratosphere they require that the mind should assure itself of its jumping-off ground and test its equipment.