19 Arguments IV – Hidden Premises

In the last homework I sneaked in an overlapping argument in which one of the arguments had a hidden premise that wasn’t stated. You might have identified that, but probably you didn’t. That’s fine, it was just a teaser meant to get you thinking. This short chapter is about just such premises.

A lot of time when we offer reasons for what we think or are trying to convince people of – i.e., when we create arguments – we leave out some of the claims that logically we are assuming and relying on to get to our conclusion. Often this is not a problem, because the context allows people to recognize our assumptions even if we don’t state them. As the saying has it, there’s no need to state the obvious.

Except sometimes there is: it can happen more often than we think that what we think is obvious and true is not so obvious to others, and may even be rejected by them. So if we are to create good arguments, we need to make sure we are clear on all the claims we are relying on to get to our conclusions.

This goes in the other direction too. When we are engaging with someone else’s argument and trying to understand and evaluate it, we need to make sure that we are clear on everything they are relying on to get to their conclusion, even if they are not explicitly stating it.

So, we need to be on the lookout for implicit or unstated or hidden premises.

Definition: a hidden premise is a claim that is logically relied upon as a premise in an argument, but that is left implicit or unstated.

Identifying hidden premises can be challenging, for this means we have to see what isn’t there. Fortunately, this is a skill you can acquire and get better at. And there are often some general rules you can follow to help identify implicit premises.

First a couple of examples of arguments that are leaving a premise out, then we’ll get to the rules.

Example 1

Suppose I tell you that I haven’t met Mel, but I know she has four legs. You ask me why I think that, and I tell you that I know that Mel is a dog. You’d probably immediately see why I would say that I know she has four legs without me having to say anything more.

If we outline it, the argument I’ve just made would look like this:

In this case, you can immediately see why that conclusion, for you know something else that isn’t stated here: that dogs are four-legged animals. “Dogs have four legs” is thus an implicit premise the initial argument relied on. It’s just such an obvious an uncontroversial claim that you could automatically understand the argument without it having to be stated. But, if we want to be crystal clear on what’s happening in the argument, we do need to state it, in which case the outlined argument looks like this:

Now, making the implicit premise explicit here might not seem worth bothering with, given how obvious it is, but, as we’ll see below, and more in chapters to come, being clear on all the premises is crucial for being able to evaluate whether an argument is successful in establishing the truth or probability of its conclusion. That’s because we need to know both how the premises logically connect to the conclusion, and whether each premise is true or not. If we haven’t identified all the relevant premises, we can’t do that.

Also, note that, even in this simple argument, you could challenge the first premise. For, though it’s rare, some dogs are born with more or fewer legs than four, and some dogs lose legs in the course of their life. So, strictly speaking, not all dogs have four legs, even if being four-legged is characteristic of dogs as a species. That means that if we really want to be precise in our argumentation, we should qualify the premise and the conclusion, in which case we get this:

If in ordinary conversation you insisted on the kind of precision this modified argument captures, nobody would want to talk to you. You’d come across as pedantic and annoying (like Socrates?).

But there are contexts where being clear and precise is important – for example, academic, scientific, medical, and legal settings – and so being able to recognize and make precise all the elements in a given argument is important. This simple initial example is just meant to illustrate how this works, even if it’s not a case where it really needs to happen.

Here’s another example where the importance of being clear on what’s being assumed is a little more obvious.

Example 2

Suppose Avery says, Cal should be sent to jail for life, and you ask Avery why they think that. Avery tells you, well, Cal killed Bob, that’s why.

So, if we outline it, Avery’s initial argument looks like this:

First note that, unlike in the first example, here the conclusion is an evaluative claim about what should be done. But the premise given in support of it is non-evaluative; it just says what Cal did.

Crucial Point: An evaluative conclusion needs at least one relevant evaluative premise.

None is stated here, so we have to think about what exactly Avery is assuming that would let them jump from Cal’s killing of Bob to their needing to be sent to jail for life.

One premise that would let Avery do this is this: anyone who kills someone else should be sent to jail for life.

If Avery believes that, then their argument makes sense. That’s a very general evaluative claim, not tied to this specific instance of killing, but, precisely because of its generality, it would allow Avery to make a judgment about the particular case of Cal and Bob.

Now, this sort of identification of hidden premises in another person’s argument is always somewhat speculative. It could be that Avery believes something else, or that they’re just expressing a knee-jerk reaction to the situation. When we are trying to understand and evaluate the arguments that other people give us, however, a general rule is to follow the principle of charity.

Principle of Charity: when trying to understand another, assume they are rational and reasonable (at least as rational as reasonable as you are), and that they are intelligent enough not to make obvious errors in reasoning.

In the case of identifying unstated premises, this means filling in the gaps in way that yields the most powerful and logical argument.

You might reasonably ask: why follow this principle, given that there are plenty of irrational, unreasonable, and ignorant (if not unintelligent) people out there?

One reason is that you probably hope people treat you this way. You don’t like it when people think you are stupid or illogical. So, it’s only fair not to treat them that way.

Another reason is that, it’s in your own interest to do so. For, if you agree with the conclusion they are arguing for, you will want to provide the most powerful argument for it, as that will be an argument you can use too. And if you disagree with it, then making sure you are challenging the most powerful argument for it means that, if you are successful, there’s less of a chance they can easily revise their argument to make it stronger.

(Looking ahead a couple of chapters: to deliberately present another’s position, claim, or argument in a way that weakens it so as to make it easier to attack, is called committing the “straw man fallacy” — the idea being that a straw man (like a scarecrow) is easier to attack and defeat than a real one.)

Back to the argument at hand. If we interpret Avery charitably and find a premise that makes their argument logical, we posit that their missing premise is that anyone who kills someone else should be sent to jail for life. If we then outline the full argument we get this:

Because we’ve identified a premise that makes the logic of the argument work — the conclusion follows from the premises — we can now ask the further question as to whether the premises are true. And, in this case, you might want to challenge that first premise. We can ask questions like, “what if Rob killed Bob in self-defense?” Or, “what if Rob and Bob were soldiers on opposite sides in a military conflict?” Or, “what if Rob accidentally killed Bob?” These are situations where we tend to distinguish legitimate killing from illegitimate, or different degrees of illegitimate killing, and so what sort of punishment, if any, is merited. Not all killing is regarded as murder worthy of life imprisonment. (These distinctions among kinds of killing are represented in our system of law. The law could, of course, be wrong. It represents a kind of evolved, collective judgment about evaluative issues. But it can be questioned and criticized and changed.)

We couldn’t ask these questions and the distinctions they represent, and so engage meaningfully in a dialogue with Avery and see if their view is one we, too, should accept, if we didn’t first get clear on what evaluative assumption was driving their conclusion about what should happen in the Cal-Bob situation.

Important note: by looking at all the reasons being given for the conclusion, we can treat that conclusion as not merely an expression of Avery’s opinion, despite its being an evaluative claim. By engaging them in their reasoning for it, we treat it as a claim that we may or may not also have reasons to accept as true. This is one of the ways in which evaluative claims are not the same as opinion claims, and the fact-opinion distinction is not the same as the distinction between non-evaluative and evaluative.

Two Rules for Identifying Implicit Premises

Let’s wrap up here with two helpful rules you can follow for seeing if there is an unstated premise and what it will look like. These won’t work in every situation, but they’ll help in enough to be worth learning.

Rule 1: When the premise given makes a claim about how something is a member of some group or class, look for an implicit general claim that describes features that all or most members of that group have.

This is what’s happening in both of the examples. The group in the first is dogs, the group in the second is the class of acts in which one person kills another. Both arguments work by applying the general claim about the group/class to a particular case.

Rule 2: If the conclusion is an evaluative claim, but no evaluative claim is explicitly stated as a premise, look for the missing evaluative claim that is being relied upon (which will often be general, as in Rule 1).

This comes from the fact mentioned already, that an evaluative conclusion always needs at least one evaluative premise.