How to map arguments from a text

To analyze something is to break it down into its constituent parts, and to analyze an argument is to break it down into its premises and conclusion. I will focus on analyzing arguments presented by other people in written form. Of course, one hears arguments in conversations all the time, and the process by which one analyses them is essentially the same as with written arguments, but it is more difficult because one does not have a “fixed target” which one can take the time to study at one’s own pace. One also can analyze one’s own arguments as well as those offered by other people, and, indeed we will have occasion to do this over the course of the term, but in doing so it is important to achieve a certain critical distance from the argument, and this is best achieved by writing it out, and then treating it as though it were written by someone else.

Finding the arguments

When trying to analyze the arguments in a given text the first step is to identify which passages contain arguments. You need to single out those stretches of text in which one or more propositions are cited as a reason to believe another. There are many ways in English to indicate that one proposition is being offered in support of another. For example, we might say “I should respect her, because she’s my mother,” or “She’s my mother, so I should respect her,” “I should respect her, for she’s my mother, or “She’s my mother; therefore, I should respect her.” In all of these cases “She’s my mother” is being offered as a premise in support of the conclusion “I should respect her.”

Some of ways this argument might be expressed:

• I should respect her, because she’s my mother.
• She’s my mother, so I should respect her.
• I should respect her, for she’s my mother.
• She’s my mother. Therefore, I should respect her.
• I should respect her; she is my mother after all.

Words like “so,” “therefore,” “thus,” “hence,” and “consequently” are often used to introduce conclusions; and words like “because,” “for,” and “since” often introduce premises. “Surely,” “certainly,” “no doubt,” and other words that signal confidence in what one’s about to say are also often used to introduce premises. Words of the sorts we’ve been discussing are sometimes called particles. Looking out for particles can help you to identify arguments and adding particles to your own writing is a good way to convey the structure of your own arguments to readers. However, all of these particles also have other uses in English, and people sometimes argue without using particles at all.

Premises and conclusions can be indicated in other ways. For example, in some contexts, one can indicate that a proposition is a conclusion by saying that it “must” or “has to be” the case, but like particles, these words have other uses as well. Or someone could be very explicit and say, “I conclude that I have to respect her, on the basis of the premise that she’s my mother.” Or, swinging from one extreme to the other, he might express the same argument by saying simply: “She’s my mother. I should respect her,” or “I should respect her. She’s my mother.” And, in most contexts, if someone said this, you would recognize that he probably meant one proposition to support the other, and you would be able to tell which was which, because you understand enough about the relations between the propositions to figure out what the author probably intends. Again, sometimes premises or conclusions can be expressed in the form of rhetorical questions: “Shouldn’t I respect her? After all, isn’t she my mother?” There is a wide variety of ways in which premises and conclusions can be expressed, and in which we are able to recognize that this is what is being done.

Identifying the Conclusion and All the Premises

Once you are confident that you have found an argument, you need to identify its premises and conclusion. In order to recognize that a passage contains an argument in the first place, you must have already noticed that at least one proposition is intended either to support or to be supported by another. Thus, you will have already identified either a conclusion or a premise. Now you need to identify any remaining premises or conclusions that there may be. In doing this keep in mind that they may be introduced with inferential particles, but that they needn’t be.

The argument may be presented in any order. For example, each of the sentences expresses the same argument as the map on the right.

Map 9:

(i) Alcohol should be illegal, because it’s a drug and all drugs should be illegal.

(ii) Alcohol is a drug, and all drugs should be illegal, so alcohol should be.

(iii) All drugs should be illegal, so alcohol should be, since it’s a drug.

In (i), the conclusion is written first, followed by the two premises; in (ii) the conclusion is written after the premises; and in (iii), it is placed in between them.

To ensure that you have found all of the premises and the conclusion, read through the passage carefully, focusing separately on each proposition—each claim that could be expressed as a separate sentence (however it is actually formulated in the passage as written). Then ask yourself why the proposition is there. Is it intended as a part of the argument or as some sort of aside? If it is part of the argument, then what role is it playing: is it meant to be supporting some conclusion, or to be supported by some other proposition?

If you are having trouble figuring out whether one proposition is intended to support another or to be supported by it, it can help to ask yourself which proposition is more obviously true? In arguments we try to establish propositions that we are less sure of by inferring them from ones that we are surer of.

Implicit Premises

You may have noticed that there’s something a bit unnatural about the three sentences we looked at above expressing the argument that alcohol should be illegal. It is unlikely that anyone making this argument would state it so longwindedly. More likely he’d simply say: (iv) “Alcohol should be illegal because it’s a drug” or perhaps (v) “Alcohol should be illegal because all drugs should be.” Both of these ways of stating the argument omit one of the premises. People often do this when they think it is obvious what premise would be needed to complete their argument and when they think the person they’re speaking with will agree to that premise. If one maps these arguments as written, here’s what one would get:

Map 9a & 9b:

Inferences B and C are non-sequiturs, whereas Inference A (in Map 9, in §2.2) is a deduction. Moreover, it is obvious what premise you could need to add to Argument B (or Argument C) to make a very strong argument (namely, Argument A).

We encountered another example of this phenomenon in map 8, above. Here is that map again:

Map 8:

Some of ways this argument might be expressed:

• I should respect her, because she’s my mother.
• She’s my mother, so I should respect her.
• I should respect her, for she’s my mother.
• She’s my mother. Therefore, I should respect her.
• I should respect her; she is my mother after all.

This map is a map of the argument expressed in different ways by each of the sentences on the right. But the argument is clearly incomplete as written. Inference A is a non-sequitur, which makes Argument A worthless. But if someone said any of the sentences on the right, you would recognize that he was giving you some reason to believe Proposition 1. This is because there’s another premise, which is plausible that when combined with Proposition 2 would make for a stronger argument as follows.

Map 8a:

In this map, Proposition 3 is enclosed in brackets to indicate that it isn’t stated in the passage we are analyzing and that we have added it ourselves, because we think that the author of the passage intended us to assume it as a premise of the argument. Such unstated premises are called implicit.

When analyzing an argument, it is important to make any implicit premises explicit—that is, to state them. This is necessary because, when you go on to assess the argument, you will need to assess all of the premises in order to determine how strong the argument is. Some arguments appear to be stronger than they are, because their weakest premises are left implicit.

Not every unstated belief held by a person making an argument is an implicit premise of that argument, nor even is every unstated belief that is relevant to the subject of the argument. We can probably imagine all sorts of reasons that the person making this argument has for believing that people should respect their mothers, but none of these reasons count as implicit premises of the argument mapped above. Something is an implicit premise only if it needs to be added to an argument to prevent one of its inferences from being a non-sequitur, and if is likely that the person making the argument intended you to assume it.

Thus, the process of finding implicit premises is closely related to the process of assessing the inference. Once you have identified the stated premises and the conclusion, you may notice that the conclusion does not follow from the premises. At this point, there are two possibilities: either the inference is a non-sequitur; or there is an implicit premise, which does make the conclusion follow from the premises. You need to use your judgment as to which is the case. Is it more likely that the author of the argument made non-sequitur or that he left one of his premises unstated? People rarely make arguments that include obvious non-sequiturs, so in such cases, it is likely that there is an implicit premise that the author intended you to assume. There are some subtle situations where it is difficult to determine whether an argument is bad or whether there is some implicit premise, and there are cases where it is hard to tell which of several different premises might be implicit; but more often than not it is very clear when someone is relying on an implicit premise and what that premise is.

Multi-Step arguments and Multiple Arguments to the Same Conclusion

In §1.3 above we saw that there are multi-step arguments, where a premise of one argument is supported by a further argument. You need to be on the lookout for this sort of structure when mapping. Here’s an example:

Jane’s visit must have been over a weekend, since she spent two full days here, and she wouldn’t have been able to do so during the week. But Rob wasn’t in town, so the visit had to be on the first weekend in July, since that’s the only one when he wasn’t here.

Map 10:

The first sentence of the passage gives us Argument A, with Proposition 1 as its conclusion, and the second sentence then gives us the remaining propositions in Argument B.

It is not uncommon in such multi-step arguments for some of the propositions to be left implicit. For example, here’s another way in which someone might express the same argument mapped above.

Jane wouldn’t have been able to spend two whole days here during the week. But the only weekend when Rob was out of town was the first one in July, so her visit must have been over that weekend.

Here Propositions 1, 2 and 4 (from Map 10) are left implicit, but it is reasonably clear that the author of the passage intended the argument expressed by that map.