>>>Is your point that swearing on the Bible would have been "more Muslim" than swearing on the Koran?
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>>Why don't they ever swear on the Constitution?
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>Why do they swear at all?
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>>How does allegiance to a religion make them somehow more trustworthy?
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>How does swearing on anything make them somehow more trustworthy?

There's the tradition. As we say, "a man is bound by his word, an ox by its horns". IOW, the very act of swearing is a public promise, for all to see. As long as that tradition bears some weight in the mind of the public, it makes sense as a means of pressure on the sworn. It's a kind of "we're watching you" message from the constituency, and a "I got the message" from the politician.

It's a social thing. My question was - why a book, and why a religious book at that?

>>How do we know they won't, at some point, put the interests of their religion over the interest as The People As A Whole?
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>How do we know they won't, at some point, put their own interests over the interest as The People As A Whole, religious or otherwise?

We know they will, we don't know how fast and how far. It's a Heisenbug.

>>Each religion, almost by definition, starts with "we are right and the others are wrong", or else they wouldn't be a separate religion in the first place.

>>So how do I know they won't be driven, sometimes, by their idea that the others got it wrong?
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>I think it is well known they are always driven by their idea that they got it right.

>That fact happens to be the reason we created a system where they need to be voted into offices, only serve for set terms, and are never given absolute power.

So they need to make money fast. The difference is the same.

>Your questions aren't very insightful.

I wasn't hoping for much of depth in this matter anyway. As you noted, most of it doesn't make much sense beyond the form. The ceremony is not a rite, not a true relation, nor expression of a relation, between an elected representative and the people. The act of oath, however, can have a deeper meaning - and then why does it have to be tied to any religion at all?