Diagramming Arguments

Diagramming Arguments – Another way to expose an argument is to diagram it. To do this, first read through and number each statement in sequence. Then draw an arrow from the statement number of the premise to the number of the conclusion as follows.

Single support:

[1] The branch manager was promoted to company vice president; therefore,

[2] he will transfer to the main office.

1-------->2

The diagram shows that statement 1 is the only support offered for the conclusion in statement 2.

Joint support:

[1] If the branch manager is promoted to vice president of the company, then he will transfer to the main office. [2] He is bound to be promoted. [3] So, he will be transferring to the main office.

1 + 2------->3

This argument offers two premises for concluding that 3. Moreover, the premises operate together in support of the conclusion. Premise 1 does not provide reason for 3 without being joined with 2. This is called joint support and their dependence is indicated by the + sign.

Independent support:

[1] Cats make good pets because [2] they are affectionate. [3] They are clean. [4] They are entertaining and [5] they do well in apartments.

The conclusion is statement 1. Notice that four distinct premises are offered in support and that these premises do not need one another to provide support. This is called independent support.

2------------>

3------------>

1

4----------->

5----------->

Joint support should not be confused with independent support. A premise provides independent support if it does not need another premise or is not needed by another premise to support the conclusion. Otherwise it provides joint support along with another premise.

Extended argument:

[1] Cats make good pets because [2] they are affectionate. [3] They are clean. [4] They are entertaining and [5] they do well in apartments. So , [6] if you want a good pent, you should get a cat.

Premises 2 through 5 support the conclusion 1. From that conclusion it is further concluded that 6.

2------------->

3------------>

1----------> 6

4------------>

5------------>

This is called an extended argument because it contains an argument within an argument.

Cats make good pets and cats make good anatomical subjects. Therefore, some good pets make good anatomical subjects. Since good anatomical subjects are in high demand in medical schools, it follows that some good pets are in high demand in medical schools.

1+ 2--------> 3 + 4--------> 5

Above we see that premises 1 and 2 support 3. Statement 3 is then combined with 4 to support the conclusion 5