Inductive vs. deductive reasoning

Inductive reasoning aims at developing a theory. It moves from specific observations to broad generalizations. Deductive reasoning aims at testing an existing theory. It moves from broad generalizations to specific observations.

Both approaches are often used in research, and it’s not uncommon to combine them in one large study.

Inductive research approach

When there is little to no existing literature on a topic, it is common to perform inductive research because there is no theory to test. The inductive approach consists of three stages:

  1. Observation
    • A low-cost airline flight is delayed
    • Dogs A and B have fleas
    • Elephants depend on water to exist
  2. Observe a pattern
    • Another 20 flights from low-cost airlines are delayed
    • All observed dogs have fleas
    • All observed animals depend on water to exist
  3. Develop a theory
    • Low cost airlines always have delays
    • All dogs have fleas
    • All biological life depends on water to exist

Limitations of an inductive approach

A conclusion drawn on the basis of an inductive method can never be proven, but it can be invalidated.

Example
You observe 1000 flights from low-cost airlines. All of them experience a delay, which is in line with your theory. However, you can never prove that flight 1001 will also be delayed. Still, the larger your dataset, the more reliable the conclusion.

Deductive research approach

When conducting deductive research, you always start with a theory (the result of inductive research). Reasoning deductively means testing these theories. If there is no theory yet, you cannot conduct deductive research.

The deductive research approach consists of four stages:

  1. Start with an existing theory
    • Low cost airlines always have delays
    • All dogs have fleas
    • All biological life depends on water to exist
  2. Formulate a hypothesis based on existing theory
    • If passengers fly with a low cost airline, then they will always experience delays
    • All pet dogs in my apartment building have fleas
    • All land mammals depend on water to exist
  3. Collect data to test the hypothesis
    • Collect flight data of low-cost airlines
    • Test all dogs in the building for fleas
    • Study all land mammal species to see if they depend on water
  4. Analyse the results: does the data reject or support the hypothesis?
    • 5 out of 100 flights of low-cost airlines are not delayed = reject hypothesis
    • 10 out of 20 dogs didn’t have fleas = reject hypothesis
    • All land mammal species depend on water = support hypothesis

Limitations of a deductive approach

The conclusions of deductive reasoning can only be true if all the premises set in the inductive study are true and the terms are clear.

Example

  • All dogs have fleas (premise)
  • Benno is a dog (premise)
  • Benno has fleas (conclusion)

Based on the premises we have, the conclusion must be true. However, if the first premise turns out to be false, the conclusion that Benno has fleas cannot be relied upon.

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Combining inductive and deductive research

Many scientists conducting a larger research project begin with an inductive study (developing a theory). The inductive study is followed up with deductive research to confirm or invalidate the conclusion.

In the examples above, the conclusion (theory) of the inductive study is also used as a starting point for the deductive study.

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Raimo Streefkerk

Raimo has a bachelor's and master's degree and has written several papers and theses. He likes to share his knowledge by writing helpful articles.

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