Deductive vs. Inductive Arguments Types of Reasoning Deductive vs. Inductive Arguments

Start with Observation A good scientist / investigator is observant. Gaining knowledge from observations is cumulative. For years, people based their beliefs on their interpretations of what they saw going on in the world with around them without testing the ideas to determine validity… not scientifically valid. This can include reading and studying what others have done in the past because much knowledge is cumulative. In Physics, Newton came up with his laws of motion basing his hypotheses on the observations and work of Copernicus, Kepler, and Galileo. Conclusions based on untested observations. Example is spontaneous generation, that simple living organisms could rise from non-living organisms. Read a couple of examples.

From Observations to Theory Need reasoning and logic to mold your observations into an acceptable theory. Valid reason flow will take you from through the process. Two major types of reasoning arguments we will discuss – deductive and inductive Have them work in groups to come up with a couple of ideas about what each type of reasoning is. Note there are some variations on how these are defined.

Deductive Arguments Arguments that claim to provide complete support for the conclusion. Arguments whose claim is that if the premises are true, the conclusion must be true Impossible to have true premises and false conclusions at the same time. These are the arguments that will ‘make your case’. Logically valid The sun is a star, the sun has planets, therefore some starts have planets All dogs are mammals, all mammals have kidneys, therefore all dogs have kidneys

Inductive Arguments Arguments that claim to provide some, but not complete, support for the conclusion. No matter how strong the argument, it is always possible for the conclusion to be false even though the premises are true. Not logically valid Can play part in discovery of truths. All swans we have seen have been white, therefore all swans are white All known planets travel about the sun in elliptical orbits, therefore all planets travel around the sun in elliptical orbits. Refer to inductive arguments to learn that triangles have angles that sum to 180.

Summary Inductive reasoning is part of the discovery process whereby the observation of special cases leads one to suspect very strongly that some general principle is true Deductive reasoning is the method you would use to demonstrate with logical certainly that the principle is true Both are used in a most investigations