CAREFUL ARGUMENT ANALYSIS: Determining the Logical Structure of an Argument

 CLARIFICATION OF LOGICAL STRUCTURE

In addition to clarifying an argument by clarifying the explicit statements in the argument and by making unstated premises and unstated conclusions explicit, there is a third very important kind of clarification involved in careful argument analysis: determining and displaying the logical structure of the argument.

We have previously mentioned two useful tools for displaying the logical structure of an argument: (a) putting an argument into standard form, and (b) showing the logical structure of an argument in an argument diagram.  In order to be able to show the logical structure of an argument in either of those ways, one must be able to determine when one statement is being given as a reason or premise in support of another statement.  This post will provide some tips and hints about how to do this.

HOW TO DETERMINE LOGICAL STRUCTURE

The primary way to determine the logical structure of an argument is to use your own understanding of an argumentative text or speech.  Which statements are being given as reasons for other statements?  Which statement(s) are being given as the conclusion(s) of the argument?  Your experiences of reading and listening to arguments gives you some ability to answers these questions.

Here are some tips for determining and showing the logical structure of an argument:

1. IDENTIFY INFERENCE INDICATORS

Argumentative passages often include words that indicate that an inference is being made.  Some words are commonly used to indicate an inference:

X thus Y

X therefore Y

X so Y

X implies Y

Y because X

Y since X

The use of such words can help you determine which statements are reasons or premises, and which statements are conclusions.  Keep an eye out for these words when you analyze an argumentative passage in a text or speech.

2. IDENTIFY LOGICAL CONNECTIVES

Statements are often composed of two or more claims that are connected by a term or phrase indicating a logical relationship between those claims.  These words or phrases words indicate the logical structure contained within a statement:

IF P, THEN Q.

EITHER P OR Q.

BOTH P AND Q.

P IF AND ONLY IF Q.

The use of such logical connectives indicates that the reasoning in that argument or sub-argument involves propositional logic. 

3. IDENTIFY QUANTIFIERS

Similarly, the use of some quantifier terms in a statement indicates that the reasoning in the argument or sub-argument involves categorical logic:

ALL As ARE Bs.

NEARLY ALL As ARE Bs.

MOST As ARE Bs.

SOME As ARE Bs.

ALMOST NO As ARE Bs.

NO As ARE Bs.

More precise quantification often uses percentage:

X % OF As ARE Bs.

4. IDENTIFY COMMON LOGICAL FORMS

If you become familiar with some common forms of VALID logical inference, then you can more easily determine the logical structure of an argument:

5. DETERMINE WHEN PREMISES WORK TOGETHER

 The above valid argument forms that have two premises and a conclusion

 

 

 

 

6. DETERMINE WHEN PREMISES ARE INDEPENDENT REASONS