Do our moral beliefs need to be consistent?

by Emrys Westacott

We generally think it desirable for our moral and political opinions to be logically consistent. We view inconsistency as a failing. Why?

I'm not talking here about consistency between a person's beliefs and their actions. Failing to practice what we preach is the sort of inconsistency we call hypocrisy, and it's easy to see why we disapprove of that. Hypocrites are less trustworthy and predictable than people whose actions accord with their stated opinions. Nor am I talking about remaining consistent over time, never altering or abandoning one's earlier convictions. That's the sort of “foolish consistency” that Emerson ridiculed as “the hobgoblin of little minds.”

I'm talking about logical consistency between beliefs. Why do we care about this? Exposing inconsistency is a standard move in many an ethical argument. Take the debate about abortion, for instance. A standard argument for viewing abortion as immoral is that it is essentially no different from infanticide, which, as it is the premeditated killing of an innocent human being, meets the definition of murder. Note the form of the argument: if you think murder is wrong, then, to be consistent, you should think infanticide is wrong, in which case, to be consistent, you should think that abortion is wrong. On the other side, a common justification for permitting abortion rests on the idea that a woman has property rights over her own body. Essentially, the argument runs: if you agree that a woman's body is her own property, then consistency requires you to accept that she can do with it as she pleases, and if you agree that the fetus is a part of her body, then consistency requires you to accept that she can do as she pleases with the fetus.

Or take Peter Singer's well-known argument for why all of us who can afford to should give more to help the needy. We all agree it would be wrong to not save someone from drowning just because we didn't want to ruin our shoes. Well, Singer argues, if we think that, then we should also accept that we have a duty to save human lives if we can do so by making similar minor sacrifices–and many of us can do this by donating our disposable income to charity. Whether these lives are close by or far away is irrelevant. Again, the underlying strategy here is an appeal to consistency. If you think x, then you ought, for the sake of consistency, to think y. Many other arguments about moral matters take this form.

But why do we value consistency? In science and in our everyday beliefs about the way things are, there is a straightforward answer. Inconsistent beliefs, taken together, form a contradiction: a proposition that has the form “p and not p.” We assume that reality does not contain contradictions (an assumption first articulated by Parmenides). So we infer that an inconsistent set of beliefs cannot possibly be an accurate description of the way things are.

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