Note: This is the first post of a four-part series on the theme of promissory obligations.

During the summer of 2015, all the main Republican presidential candidates took a solemn pledge to support the eventual nominee of their party. Although such a political pledge does not appear to be legally binding, most people would agree that it is morally wrongful to not keep one’s promises. But why? Now, let’s fast forward to the most recent Republican debate–here is an anotated transcript via the Washington Post–which took place in Detroit on March 3, 2016. At the end of this debate, Fox News anchorman Brett Baier asked Donald Trump’s three remaining challengers (Marco Rubio, Ted Cruz, and John Kasich) this question:

“Gentlemen, this is the last question of the night. It has been a long time since our first debate, seven months ago in Cleveland. A lot has transpired since then, obviously, including an RNC pledge that all of you signed agreeing to support the party’s nominee and not to launch an independent run. Tonight, in 30 seconds, can you definitively say you will support the Republican nominee, even if that nominee is Donald J. Trump?”

All three candidates promised to honor their promise—to support Mr Trump if he were to win the nomination next summer—but interestingly, they offered radically different moral reasons in support of their pledge, including consequentialism (Rubio), virtue ethics (Cruz), and Kantian reciprocity (Kasich).

• Senator Rubio, for starters, said he would support Donald Trump in the end because Trump, even with all his faults, was still a better choice than the two remaining Democratic choices, Senator Bernie Sanders and Secretary of State Hillary Clinton. In other words, Rubio offered a consequentialist or utilitarian reason for keeping his promise: Trump is less bad than the other alternatives.
• In contrast to Rubio’s consequentialist claim, Senator Cruz offered an aretaic or virtue-ethics rationale for keeping his promise to support the nominee. Specifically, Cruz said he would support Trump if he won because “I gave my word that I would.” In other words, a virtuous man is one who keeps his word.
• For his part, Governor Kasich offered a deontological or duty-based reason for keeping his promise. He said, “when you’re in the [political] arena, you enter a special circle, and you want to respect the people that you’re in the arena with.” This statement is consistent with Kantian ethics, which requires one to treat one’s rivals with equal dignity–as ends and not as means.