Undistributed middle

Overview

The Undistributed middle is a similar fallacy to Equivocation, except, instead of conflating definitions, two different things are equated due to a common middle ground that is misused. The argument is assuming that the set of Object-A that has the middle ground intersects with the set of Object-B that has the same middle ground.

Examples

Here are some examples of the undistributed middle:

• Example 1

1. All cats use air.
2. All gasoline engines use air.
3. Therefore, all cats are gasoline engines.

• Example 2

1. Science uses the word Theory.
2. Creationism uses the word Theory.
3. Thus, Creationism is science.

• Example 3

1. All fish swim in the ocean.
2. All whales swim in the ocean.
3. Therefore, all whales are fish (They're not - they're mammals)