Promises come in degrees. A promise to pay back five dollars is less serious than a promise to care for a friend’s child. A promise to cook dinner is far less serious than a promise to guard a president’s life. We can think of vows and oaths as the most serious types of promises. These promises often involve important responsibilities and are usually made in a public, ceremonial fashion. For instance, US presidents take an oath of office at an inauguration ceremony. Married couples usually commit to one another at a public wedding in which they exchange vows. While oaths and vows are essential and important, they are often fraught with uncertainty, ambiguity, and danger. Here I argue that these frightening features are a necessary element of all serious promises.

Consider how oaths differ from ordinary promises. In many cases, the breach of an ordinary promise is forgivable. Say Hank has promised his spouse that he will clean the kitchen, yet forgets. His spouse will be upset with him, but will also likely forgive him if he sincerely apologizes. On the other hand, if Hank breaks his wedding vows, his spouse will not forgive him as easily. Likewise, there are conditions under which we would forgive a political leader for failing to deliver on a campaign promise. But we are unlikely to forgive that same leader for an overt act of treason. An act of treason would be a direct violation of their oath of office.

Additionally, persons tend to identify with oaths in ways that they do not identify with ordinary promises. There is a sense in which taking an oath creates a new identity. In taking an oath of office, a person becomes a mayor, governor, or president. In assenting to wedding vows, one becomes a spouse. To breach an oath, then, is to act contrary to the identity that one has chosen for oneself. The breach is a serious matter.

These two features of oaths highlight why oaths are essential and important. First, there are some social statuses that we take to have great significance. The positions of president, soldier, or attorney are essential to a well-functioning nation. We want assurance that persons who occupy these positions will do so faithfully and consistently. The oath serves as a guarantee that the person taking the oath will not violate our trust. Thus, an actual violation is a serious matter. Second, oaths are personally significant because they allow us to express our deep commitment to a cause, office, or person. Wedding vows, for example, allow romantic partners to commit to one another in ways that cannot be captured by ordinary promises.

While essential and important, oaths can give rise to moral and personal tension. An oath may obligate persons to undertake actions that they would otherwise avoid or actions that they find morally compromising. In this way, oaths are dangerous. For instance, consider the following three scenarios and related questions:

1. A soldier has taken an oath of enlistment, by which he swears to follow the orders of his president and commanding officer. He finds himself under the command of a corrupt and selfish president who orders him to fight in a war that he finds unjust. Is the soldier required to fight in the war? Would he act wrongly in violating his oath?

2. A married couple has vowed to remain in the relationship “for better or for worse . . . in sickness and in health.” Does this vow require the wife to stay with the husband after learning of his affair? Does the vow require the wife to stay with the husband after he develops severe Alzheimer’s disease?

3. A man takes an oath to follow the commands of a god. In exchange, the god blesses the man with riches, fame, and health. One day, the god commands the man to murder his spouse and children. Would the man act wrongly in disobeying this command? In obeying it?

Oaths give rise to tensions because they are binding in ways that ordinary promises are not. The list of acceptable excuses for breaking an ordinary promise is long. Bad weather, sickness, and a family emergency can all serve as excuses for not making good on a promise. The related list for oaths is short, if it exists at all. Further, one can never be sure what one has agreed to in taking an oath. The content of an ordinary promise is relatively straightforward. A promise to pay back fifty dollars is just that. But the content of an oath of loyalty is indefinitely open-ended and thus potentially dangerous. Loyalty may require any number of actions that were not contemplated at the time that the oath was taken.

One may think that these drastic moral tensions are not a necessary feature of oaths, that they can be avoided. After all, an oath can be renounced. While this is true, breaching or renouncing an oath can carry steep penalties. To breach an oath to a god is to incur criticism from one’s religious community, and, even worse, to incur the wrath of that god. To renounce one’s oath as a soldier is to give up one’s identity as a soldier, and, perhaps, to face steep penalties from the government. And, to renounce one’s wedding vows is to give up on a marriage and one’s identity as a spouse. Thus, one can escape the duties entailed by an oath, but not without great cost. Breaking an oath can undermine one’s self-image and can be attended by steep social and legal penalties. In short, a solemn promise, an oath, is treacherous because it entails a great social and personal commitment that cannot be easily waived.

Alternatively, one may believe that the treachery of oaths can be avoided not by abrogating the commitments entailed by an oath, but by subjectively determining what those commitments are. One who follows this strategy would, in each instance, decide whether some course of action was required by their oath. The soldier in the above case would determine for himself whether his oath required him to go to war. The wife in the above case would consult her own judgment to determine whether she is obligated to stay with her cheating husband. Finally, the man who has committed himself to a god would selectively determine which of the god’s commands he was bound to obey.

In this way, it seems, the oath takers could maintain their identity and commitments, yet avoid any actions they deem problematic or unsavory. While seemingly promising, this strategy will not work either. To see why, we must first think in more detail about what it means to make a promise or to undertake a commitment. To promise or to commit oneself is to agree to be governed by certain norms. For instance, to agree to build a house is to agree to undertake those actions that constitute building a house. These actions are normative because one could either succeed or fail in undertaking them. They are also normative in that one can be praised or blamed for undertaking or failing to undertake them.

In short, there is a right way and a wrong way to fulfill a promise or an oath. If there was no right way to fulfill an oath, oaths would not be normative. Put differently, if anything counted as fulfilling an oath, nothing would so count. Under the current proposal, the oath taker subjectively determines the content of the oath, what is right and wrong according to the oath. This strategy is doomed to fail because if what is right according to an oath is simply what the oath taker believes is right, then there is no sense in which the oath taker is bound by a norm. In this case, anything goes!

This is a point that was emphasized by philosopher Ludwig Wittgenstein. As Wittgenstein argues, there can be no private language—that is, a language governed by norms that are determined exclusively by a single person. Such a language, he argued, would have no norms and thus would not be a language. The point I make is similar: there can be no private oaths. To commit oneself by taking an oath is to commit oneself to something external, an external standard by which one’s actions can be judged. Thus, this second strategy will not work. Oaths are treacherous partly because their demands necessarily outstrip our subjective understanding.

We can ask where the content of oaths comes from. Following Wittgenstein, I believe that the content comes from a community of persons who agree upon and extend the meaning of any particular oath. The extent to which a soldier must be loyal to a president is determined by a political community. The degree of faithfulness one owes to a marriage is determined in part by the married couple themselves, but also by the married couple’s community. Commitments to deities are harder to understand. I tend to think that these commitments are determined by religious communities, but I will leave that question to the theologians.

Given that oaths are treacherous, that they may require us to do things that make us uncomfortable, one might conclude that it is better to avoid these solemn promises altogether. But, one need not draw this conclusion. We rightfully seek assurance that persons who hold vital social positions will execute their duties faithfully. Additionally, part of being human is making strong commitments about the content of one’s character and about one’s loyalty to other persons or causes. We would not want to live in a world without oaths. While oaths should not be avoided altogether, one should think long and hard before taking an oath. An oath can lead to places that one could never imagine.