But cannot the believing Christian submit to scientific investigation the doctrine of faith itself, which he must without doubt hold to be true? This must surely be allowed if he is to convince himself scientifically of the truth of it. Indeed, this is allowed. He may critically examine everything to the very bottom, even the existence of God, the rationality of his own mind. But how can he, if no doubt is permissible? To examine means to search doubtingly; it means to call the matter in question—this, too, is right. It is, on the one hand, a doctrine of the Catholic Church that they who have received faith through the ministry of the Church, that is, they that have been made familiar with the essential subjects of the faith and the motives of their credibility by proper religious instruction, must not doubt their faith. They have no reasonable excuse for doubting because they are assured of the truth of the faith. We have discussed this point before.(4) As a matter of course only voluntary doubts are excluded, doubts by which one assents deliberately and wilfully to the judgment that perhaps not all may be true that is proposed for our belief. Involuntary doubts are neither excluded nor sinful. These are apparent counter-arguments, objections, difficulties against the faith, which occur to the mind without getting its conscious approval. They are not unlikely, because the cognition of the credibility of Christian truths, while it is certain, is yet lacking in that obvious clearness which would render obscurity and counter-argument impossible; the assent to faith is free. Doubts of this kind are apt to molest the mind and buzz round it like bothersome insects, but they are not sinful because they do not set aside the assent to faith any more than the cloud that intervenes between us and the sun can extinguish its light. The assent to faith is withdrawn only when the will with clear consideration approves of the judgment that the doubt may be right. But what about doubts which one cannot solve? Would we not owe it to truth and probity to withhold assent to faith for a while?