Combining Induction and Deduction: Claims, Supports, Warrants

Induction and deduction are primary forms of reasoning, each an intellectual procedure based on human experience generalizing from particulars, applying generalities to particulars. Each supports the other. When we compose arguments in everyday life, moreover, we're likely to use both reasoning processes, as we use both our hands.

We've already seen that inductive conclusions can become the major premises of deductive arguments. Just as easily, induction can provide us with minor premises. One of the best-known examples of inductive support for a minor premise is in the Declaration of Independence. In this classic argument, Thomas Jefferson builds the case for American autonomy from a major-premise assumption and a minor premise supported by extensive evidence:

Major premise: People have the right to abolish tyrannical governments.

Minor premise: The government of King George III is tyrannical.

Conclusion: The people of the Colonies have a right to abolish the government of George III.

Having asserted his assumptions about basic human rights, Jefferson goes on to cite the "history of repeated injuries and usurpations" of which the Crown is guilty. The conclusion—if we grant the premises and the accompanying support—is, and was, inescapable

We find inductive and deductive logic combined in almost every form of knowledge, as we support our conclusions with both evidence and general assumptions. Scholar Stephen Toulmin describes the everyday occurrence of such reasoning in his claim-support-warrant system of argument:

• The arguer presents a claim or proposition

• He or she supports the claim with data (such as facts and the opinions of experts—inductive evidence) or other reasons.

• The advocate ties the claim and support together with an underlying warrant or general principle that relates them (like the major premise of a syllogism). This form of argument includes qualifiers, limits to keep claims from going beyond what the data can reasonably support.

Most arguments, then, will include these elements

• The claim or main proposition

• Evidence: specific data, either fact or opinion, gathered to back the claim. Such evidence may be in the form of testimony: statements by witnesses and experts, or as documented information facts that can be verified by other sources.

• Reasons or motivational appeals: appeals to the audience's needs, values, beliefs, or common sense, including explanations and analyses.

• Assumptions or warrants: general principles taken for granted, believed to be true without additional proof. They may be stated explicitly or left unstated.

• Qualifiers: limits on the claim.

Here's an example of a claim-support-warrant argument:

Claim: Regular exercise contributes to cardiovascular fitness.

Data: Published findings in medical journals, testimony by physicians.

Other support: Testimony from heart patients who've added exercise to their daily routines.

Warrant: Most scientific studies and medical opinions are reliable

Qualifier: "Contributes to" implies that other factors are also necessary for cardiovascular fitness.

The claim-support-warrant method acknowledges that, in everyday life, people don't always construct arguments according to strict formulas. Rather, they make assertions (claims) and attempt to support them with any evidence and reasons that seem appropriate or convincing. We support our claims with information and explanation. We try to justify our positions by showing that they're based on solid facts and meaningful interpretations of those facts.