Earlier this year, an environmentalist serving on a jury took the oath by swearing on a river. Jurors are legally permitted to swear on their own religious book, as well as to make a non-religious “affirmation” instead of taking an oath, but this was reportedly the first time someone has sworn an oath on a part of nature. This juror swore with his fingers dipped in a cup of water taken from his local river. He explained that nature was his god and that he treated the river with the same “reverence, sacredness and love in action as many religious people give to their holy book.” Religious oaths are classified by the Westminster Confession as a part of worship, differing from activities such as preaching and the sacraments only in that they are “occasional” (appropriate on specific occasions) rather than “ordinary” parts of worship. Oaths are often discussed by theologians as an implication of the third commandment, “Thou shalt not take the name of the Lord thy God in vain …” As the following updated excerpt from James Durham’s work points out, one key reason for treating an oath as a part of worship is that you cannot swear by the name of someone you can’t pray to. When a juror swears by Almighty God, they are calling Almighty God to witness what they are swearing, and to judge them according to the truth or falsehood of what they swear. On this view, to call on someone or something that is not the true God is worse than futile.

The Third Commandment both requires oaths, and requires oaths to be kept.

What is an oath?

At the outset we would like to distinguish between these four things.

Oaths are sayings which directly invocate God by expressions such as ‘By …’ (‘By my holiness I have sworn,’ Psa. 89:35), or, ‘I swear by the Lord.’

Asseverations (also called vehement assertions) are expressions such as, ‘As the Lord liveth,’ ‘In conscience,’ ‘In faith,’ &c. Like oaths, these should be done in truth and judgment with fear, and when called to, but they differ in that, in oaths, we are only to make mention of the true God, and swear by Him, but asseverations may be expressed in terms such as, “As thy soul liveth” (2 Kings 2:2, 4, 6), and yet by so saying we do not swear by the soul of anyone.

Simple assertions, such as, ‘In truth,’ ‘Truly,’ ‘Indeed.’ These only speak the thing simply, and affirm what is asserted to be true or false. As such, these belong to the Ninth Commandment only.

Imprecations are either directed to oneself conditionally, such as, ‘If such and such a thing is truth, then let me perish;’ ‘Shame upon me, if I do not do this or that;’ or they are directed towards others, especially in things like, ‘Shame upon you,’ ‘the devil take thee,’ ‘vengeance on thee,’ and other expressions too abominable to mention.

Thinking in more detail about oaths. In oaths which are for confirmation, we distinguish between assertory oaths, which only confirm a thing to be truth, and promissory oaths, which engage the person swearing to perform a certain thing in the time to come, either absolutely or with qualifications.

When an oath has the right qualifications, either of these kinds of oath is a lawful piece of God’s worship, and may, and should, be made use of by His people. This is a clear truth from Scriptures such as Deuteronomy 10:20; Deuteronomy 6:13; Jeremiah 4:2.

What is the right way to swear an oath?

What can we swear about?

Consider, first, the matter of an oath. Assertory oaths must be about things that are (1) true; (2) weighty; (3) true and weighty to our knowledge. Meanwhile, promissory oaths must be about things which are (1) just and lawful, (2) possible, (3) profitable, (4) in our power, and (5) all of these to our knowledge.

What form should it take?

The form of an oath must be, “By the true God …” Swearing an oath is a special part of God’s worship, for we can swear by no one whom we cannot invocate. Therefore idols, creatures, graces, &c., are excluded here, for none of these are God.

When is an oath called for?

The impetus to swear an oath must be edification, that is, God’s glory, our own vindication, or our neighbour’s good, or the call of a magistrate putting us to it. The oath should be used for putting an end to controversies, when no other means of clearing up or deciding them remains.

What kind of expressions should we use?

As to the expressions in which the thing is sworn, it is required not only that it be truth to the person who swears it, and true in that person’s meaning, but also that the expressions are plain and intelligible to the meaning and understanding of the person to whom the oath is given, otherwise it deludes rather than clarifies.

Hence these two rules are to be observed.

1. The meaning must be so clear that it may be, and is, most ordinarily and obviously gathered from the words and expressions that are used.

2. The expressions must be according as they are supposed to be understood by others, especially the one who requires the oath. If he means one thing, and we another, then God’s name is profaned, and the point of the oath is frustrated. Needless to say, equivocations in our expressions, and mental reservations, are condemned. Equivocation means using ambiguity in our words; mental reservation is when we privately give the words a different sense in our thoughts from what they seem to mean to anyone else.

How do we go about it?

As to the right manner of swearing, these things ought to be noticed.

We must swear intelligently. It must be in judgment; we must understand the thing we swear, and the nature of our oath, and the God we swear by (Jer. 4:2).

We must swear with godly fear and reverence. We are now in an especial way in God’s own sight, and it is good if the heart would be filled with the sense that God is present.

We must swear in integrity. There must be single-mindedness in our aim, that it would not be to deceive anyone, but to express the truth truly and faithfully (this is called righteousness in Jeremiah 4:2.

And for the most part these properties or qualifications may agree to oaths, asseverations and imprecations.

What can we not swear by?

What then may we judge of oaths that people swear by angels, saints (“by Mary,” “by Paul”) and other created things (such as heaven, light, the world), by soul, conscience, &c., or by graces, such as, “by faith”?

We need not be too particular in drawing distinctions here, for we conceive them all to be simply unlawful.

That is partly because none of these are God, and swearing is a special piece of God’s worship (Deut. 6:13). Swearing by any thing, whatever it is, which is not God, is condemned: “They have sworn by those who are not gods” (Jer. 5:7).

It is partly also because we cannot invocate any of these, and therefore we cannot swear by them. An oath carries along with it an invocation, or calling on the name, of the one we swear by.

Also, these other persons or things lack the properties of the one to whom this worship belongs. They lack, for example, omniscience, to examine whether we mean what we have sworn or not, and omnipotence, and justice to avenge, if things are not as we have sworn, and the sovereign right to call the swearers to a reckoning. It would also derogate from the thrust of this commandment, which gives this honour to God alone, as His due, and implies that He alone has all these properties in Him.

Indeed, such oaths are expressly prohibited by Christ. “Swear not at all, neither by heaven nor earth” (Matt. 3:34), for they stand in an inferior relation to God, and are His servants.

As none of these things are God, to take order with us if we swear falsely, so none of them are ours, so as we can lay them in pledge, for the least thing to be done to them if our oath is not true. None of them can be added to or diminished from by us. We cannot make one hair of our heads black or white, which is why we ought not to swear by our head. Much less can we quiet our conscience, or increase our faith, that we should so freely swear by these. Matthew 5:36 makes this clear.

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