A single theme runs through the three essays on St. Thomas gather in this book. It isthe theme of mystery or, more exactly, the response of the searching human intellect to the fact of mystery. Both the fact and the response are suggested in a short biography of St. Thomas that forms the first essay and are then sketched out in detail by a presentation of the Anegative element in his philosophy. The third essay shows that contemporary Existentialism is in basic agreement with the philosophia perennis on this fundamental element of philosophical thinking. AEmphasis has been placed not so much on the positive attainments of philosophical thought, Pieper says in conclusion, Abut rather on a no less important aspect: namely, that man, in his philosophical inquiry, is faced again and again with the experience that reality is unfathomable and Being is mystery B an experience, it is true, which urges him not so much to communication as to silence. But it would not be the silence of resignation, and still less of despair. It would be the silence of reverence.