...we are reminded by how far today we are afflicted by a certain kind of provinciality of mind, a reductivist mentality that can conceive of a question's being worth asking only if we know in advance some routine procedures guaranteed to provide intelligible answers to it. It is indeed an exceedingly curious reversal of commonsense intellectual priorities that a pre-formed procedure for answering questions should be allowed to dictate the legitimacy of the questions that may be asked. Thomas is intellectually braver, even perhaps more irresponsible: there are for him questions that have to be asked, but cannot be answered. He is prepared to ask the question: Could everything's being like the daffodil—“contingent” is his word for the fragility of existence—be just a fact, a sort of brute fact, requiring no further explanation? Or must everything's being like that demand an explanation, a cause, whose hold on existence does not need to be accounted for?—his word for such a mode of existence being “necessary.” Thomas's answer to that last question is in the affirmative: it has to be the case that some necessary being exists, otherwise the existence of all the contingent beings that there are is impossible to account for.
From Thomas Aquinas: a Portrait, by Denys Turner