Let me offer this in that regard. Technically and logically speaking, you're quite right. If you ever want to prosecute under the Criminal Code, perhaps that has to be there.
But go to the dynamics of each meeting. I can remember many meetings where if the witness was already very nervous and apprehensive about the event and you then put a Bible in front of them—this might be enough to put them over the edge in some cases.
But you have to ask yourself, what are the realistic prospects that you're ever going to seek a criminal prosecution for perjury? My view is in 99% of the cases where there might be a basis for false testimony, you're going to report to the House and go that route, as opposed to asking the Attorney General to use his or her discretion to prosecute and perhaps involve members of the committee as witnesses in a criminal prosecution. I don't see that.
So my short answer, Mr. Chair, is yes, you should swear in every witness, just in case you get one person against whom you want to lay charges for perjury. But weigh this against the formalism it would bring into the process.
In parliamentary terms, common law terms, every witness is obliged to speak the truth and all the truth to a parliamentary committee, failing which the House can hold them in contempt. The House has its own remedies for this, although it has rarely happened.