3/9 3. Argument Structure

The Basic Structure of an Argument

An argument is a structure of reasoning in which one or more propositions support another proposition. The supporting propositions are premises, and the proposition they are meant to establish is the conclusion. The movement from premises to conclusion is an inference.

For example:

The library is closed on Sundays. Today is Sunday. Therefore, the library is closed today.

• Premise 1: The library is closed on Sundays.

• Premise 2: Today is Sunday.

• Conclusion: The library is closed today.

The central question is not whether people disagree. It is whether some claims are being offered as reasons for accepting another claim.

Takeaway: Identify the claim being supported and the propositions offered to support it.

Premises, Conclusions, and Linked Support

A premise provides evidence, a reason, or a justification. A conclusion is the claim that the arguer wants the audience to accept. Arguments can contain one premise, several independent premises, or linked premises that work together.

Consider the linked-premise example:

All mammals are warm-blooded. Whales are mammals. Therefore, whales are warm-blooded.

Neither premise alone establishes the conclusion. Their combination supplies the relevant support. In longer arguments, a conclusion can also become a premise for a later conclusion. For example:

1. The roads are icy.

2. If the roads are icy, driving will be dangerous.

3. Therefore, driving will be dangerous.

4. If driving will be dangerous, the school should close.

5. Therefore, the school should close.

Here, proposition 3 is an intermediate conclusion: it is supported by the first two propositions and then supports the final conclusion.

Takeaway: Map not only the final conclusion, but also any intermediate conclusions and relationships among premises.

Recognizing Premises and Conclusions

An indicator word can suggest the role of a proposition, but context determines the actual structure. Common premise indicators include:

• because

• since

• for

• given that

• as

• seeing that

• on the grounds that

• as indicated by

Common conclusion indicators include:

• therefore

• so

• thus

• hence

• consequently

• accordingly

• it follows that

• for this reason

• this shows that

For example:

Since regular exercise improves cardiovascular health, and walking is a form of regular exercise, walking can improve cardiovascular health.

Here, since introduces a premise and the final clause is the conclusion. But conclusions do not always come last:

Walking can improve cardiovascular health because walking is a form of regular exercise and regular exercise improves cardiovascular health.

To locate the conclusion, ask: What claim is the writer trying to establish? Then ask: Which claims are being offered as reasons for it?

Takeaway: Use indicator words as clues, not as automatic labels.

Reconstructing Informal Arguments

Reconstructing an argument makes informal reasoning easier to analyze while preserving its intended meaning. Use this procedure:

1. Identify the main claim: what does the speaker want the audience to believe?

2. Locate the supporting reasons.

3. Separate premises from conclusions.

4. Supply a missing premise only when the reasoning clearly depends on it.

5. Arrange the propositions clearly, usually by numbering the premises before the conclusion.

6. Preserve the original strength and scope of the claims.

Example:

You should take an umbrella—the forecast predicts rain, and you do not have a raincoat.

A reasonable reconstruction is:

1. The forecast predicts rain.

2. You do not have a raincoat.

3. If rain is predicted and you do not have a raincoat, you should take an umbrella.

4. Therefore, you should take an umbrella.

The third proposition makes explicit the assumption connecting the stated reasons to the recommendation. A fair reconstruction should use claims the speaker would likely accept, avoid unnecessary controversial assumptions, and distinguish what was stated from what the analyst supplies.

For instance, if someone says that a medicine helped several patients and may be useful, reconstruction should not replace that qualified claim with the much stronger claim that it will cure everyone.

Takeaway: Clarify implicit reasoning without strengthening, weakening, or distorting it.

Validity, Soundness, and Support

In a deductive argument, valid describes the connection between premises and conclusion. An argument is valid when it is impossible for all the premises to be true and the conclusion false at the same time.

A valid form is:

1. If the alarm is set, the light will flash.

2. The alarm is set.

3. Therefore, the light will flash.

If the premises are true, the conclusion must be true. By contrast:

1. If the alarm is set, the light will flash.

2. The light is flashing.

3. Therefore, the alarm is set.

This form is not valid because something other than the alarm could have caused the light to flash.

A sound argument is valid and has true premises. Keep these questions separate:

1. Are the premises true or acceptable?

2. Do the premises adequately support the conclusion?

An argument may have a valid structure even when a premise is false. Conversely, a conclusion may be true even when the argument offered for it is weak.

Takeaway: Evaluate both the truth or acceptability of the premises and the logical support connecting them to the conclusion.

Arguments and Explanations

An argument reasons toward a conclusion that the audience may not yet accept. An explanation starts with a fact or event treated as accepted and tells why or how it occurred.

Compare these examples:

The streets are wet, so it probably rained last night.

This is an argument: wet streets are offered as evidence for the conclusion that it rained.

It rained last night, which explains why the streets are wet.

This is an explanation: the rain is treated as known, and its connection to the wet streets is being described.

The distinction depends on context. “The engine stopped because it ran out of fuel” is usually an explanation when the engine’s stopping is already accepted. It may function as an argument when the lack of fuel is being used as evidence for why the engine stopped.

Takeaway: Ask whether the speaker is trying to establish a claim or account for a claim or event already accepted.

Non-Arguments and Purpose

Related sentences do not automatically form an argument. The following are generally non-arguments when they do not offer inferential support:

• Descriptions: “The building has three floors and a glass entrance.”

• Reports: “The committee met on Tuesday.”

• Questions: “Did the train arrive?”

• Commands: “Close the window.”

• Exclamations: “What a beautiful view!”

• Conditional statements alone: “If the temperature falls, the water will freeze.”

• Lists: “Apples, oranges, and bananas are available.”

A conditional statement can be part of an argument, but by itself it does not establish either its antecedent or its consequent. It becomes part of an argument when combined with additional premises and a conclusion.

The practical test is purpose: is the passage attempting to prove or establish a claim, explain an accepted fact, describe something, ask a question, issue a command, or express an attitude?

Takeaway: Look for inferential support rather than assuming that every group of propositions is an argument.

A Complete Method for Argument Analysis

Use this checklist to analyze an unfamiliar passage:

1. Find the main point. What is the author trying to establish?

2. Look for support. Which claims are offered as reasons?

3. Check indicator words. Do terms such as because or therefore suggest the structure?

4. Test the purpose. Is the passage proving a claim, explaining an accepted fact, or merely describing something?

5. Identify missing assumptions. What must be added for the reasoning to make sense?

6. Map the structure. Mark premises, intermediate conclusions, and the final conclusion.

7. Evaluate the connection. Do the premises support the conclusion? If the argument is deductive, is its form valid?

Worked example:

The museum should extend its hours. Attendance has increased every year, and many visitors cannot arrive before 5 p.m. Therefore, extending the hours would allow more people to visit.

A reconstruction is:

1. Museum attendance has increased every year.

2. Many visitors cannot arrive before 5 p.m.

3. Extending the museum’s hours would allow more people to visit.

4. Therefore, the museum should extend its hours.

The first two propositions are premises. Proposition 3 is an intermediate conclusion supporting the final policy recommendation. The passage is an argument because it offers reasons intended to establish what the museum should do.

Final takeaway: Good analysis identifies the purpose and structure of a passage before judging the truth of its premises or the strength of its support.