Inductive and Deductive Logic Philosophy

Overview According to traditional logic, arguments can be either inductive or deductive. Sometimes it is difficult to determine which category an argument might be in. There are some key concepts that give clues as to which type the argument is.

Definitions Inductive Logic: Usually described as moving from the specific to the general Arguments based on experience or observation are usually expressed inductively Deductive Logic: Usually described as moving from the general and ending with the specific Arguments based on laws, rules or other widely accepted principles are best expressed deductively.

Explanation The difference between inductive and deductive reasoning is mostly in the way the arguments are expressed. Any inductive argument can also be expressed deductively, and any deductive argument can also be expressed inductively. Each also requires different sorts of support Inductive argument is supported by previous observations Deductive argument is supported by rules and laws, regardless of observation

Example 1 Which of the following claims would best be expressed by inductive reasoning? A. Your first quiz grade usually indicates how you will do in the course B. The final exam accounts for 30% of the course C. Late papers will not be accepted D. is required reading in your courseGravity’s Rainbow

Example 2 Which of the following claims would be best expressed by deductive reasoning A. California’s population growth rate slowed last year B. California residents appreciate their good weather C. California residents are residents of the United States D. More cars are registered in California than any other state

Example 3 Which of the following arguments would lead to a deductive conclusion? A. There was a mild winter this year; previously whenever there’s been a mild winter the cherry crop suffers B. The cherry crop needs at least a week of freezing temperatures for best results, and this winter the temperature stayed several degrees above freezing C. Primo noticed that whenever the skiing was good in the winter, the cherry crop was profitable and this year the skiing is good D. Not since 1972 have I seen a good cherry crop after a mild winter, and this winter has been mild

VALIDITY??? Inductive arguments can not be tested for validity Inductive arguments are stronger or weaker based on the quality of the reasoning, experience, analogy, or generalization Only Deductive arguments can be tested for validity

Inductive Logic Philosophy

Inductive Arguments Inductive arguments are usually based on experience or observation. In effect, inductive arguments are comparisons between two sets of events, ideas, or things. Sometimes are called analogical arguments See the example on packet page 13

Because were argue inductively from the particular to the general, such arguments are often called generalizations, or inductive generalizations. Other kinds of arguments with similar format include causal arguments. Inductive reasoning attempts to predict or suggest its conclusion based on inferences on the premises, but there is no necessity for the conclusion to follow the premises. In other words, there is no guarantee that the future will be like the past.

Inductive reasoning does not aim at producing true, valid conclusions. In fact, “valid” and “invalid” are not terms that can be accurately applied to inductive reasoning. They can only be weak or strong Inductive reasoning enables us to infer probable and likely conclusions. Useful for gaining new knowledge by understanding statistical patterns and also for identifying causes and effects. The two most common types of inductive argument are the analogy and the statistical

Deductive Logic

Deductive Arguments Deductive reasoning moves from particular facts, analogies, common threads and connections to a conclusion based on the evidence Generally, deductive arguments are ones wherein the conclusion validly follows from the premises. The most common form of a deductive argument is that of the syllogism A syllogism consists of two premises and a conclusion The conclusion is a proposition that follows from other premises. The conclusion is supported by the other premises.

Deductive arguments must follow certain rules to be valid. Deduction aims at producing true, valid conclusions, but if one of the premises is false, the conclusion will be false. Take the following example, for instance: Some dogs are ill-behaved. All dogs are animals. Therefore, all dogs are ill-behaved. Is the conclusion valid? Why or why not?

Let’s look at more examples of syllogisms Let’s look at more examples of syllogisms! Turn to your packet page 14 