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Digital thinking tools for better decision making
Digital thinking tools for better decision making

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2.2 The importance of a good base

You can think of an argument map as a tipped-over pyramid (see Figure 4). At its pinnacle sits the main claim. The map records both supporting and opposing claims for that main claim. At its base are the claims for which no further support or opposition is provided.

A schematic representation of a tipped-over argument map, shown as an equilateral triangle.
Figure 4 A schematic representation of a tipped-over argument map

For your argument to be effective, the base must be solid. It carries your argument. If the base is dubious, your audience is unlikely to accept the argument. For that reason, the base needs to consist of claims that the audience will readily accept.

One way to do this is to have a base that consists of claims that

  • a. you believe
  • b. your audience also believes.

In other words, the claim needs to be accepted already by you and your audience. You cannot make a case based on a claim that you disagree on with your audience.

For example, you may choose a claim for your base because it is uncontroversial. This means that not only do you and your audience believe it, but also the wider community you belong to. Such information is referred to as facts or common knowledge. For instance, in your map, the claim that ‘Carrots are a source of vitamin A’ falls into this category.

Another way to make a solid base is to provide the audience with claims that express trustworthy evidence. For instance, evidence from a reputable scientific study. Such evidence may not be (and often isn’t) common knowledge, but your audience may still accept the claim. They may accept it based on the reputation of the source. An example of a reputable source is a paper that has been published in an academic journal that uses peer review. A journal with peer-reviewed or refereed papers only publishes a study if other scientists, different from the authors, have checked the research and approved it for publication.

Activity 2 Building a base

Timing: Allow about 10 minutes

The argument map you have constructed so far (Figure 3) has a rather weak base. Can you strengthen the base by selecting the correct supporting claims, choosing between:

(a) A paper published in 2003 by researchers at Brigham and Women’s Hospital, Harvard University and several other institutions reported a study in which a large group of healthy US male physicians were given beta carotene pills for 12 years. The researchers found that they had the same rate of age-related cataracts as those given a placebo (Christen et al., 2003).

(b) In 1998, researchers at Johns Hopkins and Nepal Eye Hospital Complex reported a study with 30,000 women in South Asia at high risk of vitamin deficiencies. They found that a group received vitamin A supplements had a lower risk of night blindness than a group that received a placebo (Christian et al., 1998).

In the map below, delete the incorrect option (a) or (b).
HighlightedEating carrots improves your eyesight
HighlightedCarrots are a source of vitamin A.HighlightedTaking vitamin A can reduce the risk of poor vision in individuals with a vitamin deficiency.HighlightedCarrots are a source of beta carotene.HighlightedBeta carotene supplements will not strengthen eyesight or slow decline in healthy people.
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Words: 0
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Node (a) reference: Christen, W. G., Manson, J. E., Glynn, R. J., Gaziano, J. M., Sperduto, R. D., Buring, J. E., Hennekens, C. H. (2003) ‘A randomized trial of beta carotene and age-related cataract in US physicians’, Arch Ophthalmol, 121(3), pp. 372–378.

Node (b) reference: Christian, P., West Jr., K. P, Khatry, S. K., Katz, J., LeClerq, S., Pradhan, E. K., Shrestha, S.R. (1998) ‘Vitamin A or β-carotene supplementation reduces but does not eliminate maternal night blindness in Nepal’, The Journal of Nutrition J. Nutr., 128(9), pp. 1458–1463.

For each of the claims ‘Taking vitamin A can reduce the risk of poor vision (…)’ and ‘Beta carotene supplements will not strengthen eyesight (…)’ try out a dialogue. Start with the claim ‘Taking vitamin A (…). Ask ‘What’s the evidence for that?’ and try out both continuation (a) and (b):

Described image
Figure 5 The argument ‘Taking vitamin A can reduce the risk of poor vision (…)’


Your map should now look like this.

An argument map of ‘Eating carrots improves eyesight’
Figure 6 The map

Note how each of the two pieces of evidence (starting ‘In 1998 …’ and ‘A paper …’) states findings which have been generalised (omitting some detail) in the claim they support.

For instance, the claim ‘Taking vitamin A’ can reduce the risk of poor vision in individuals with a vitamin deficiency’ is supported by findings from the study by researcher at Johns Hopkins and the Nepal Eye Hospital Complex. However, the study is only concerned with women from a specific geographical region (Asia). And it looked only at night vision (which is only one aspect of vision in general).