Notes on Introduction to Logic -- Phil A101

William Jamison - Instructor

Lecture 5:

Sorites

Question posed to a salesperson at a green house: Are any of these roses able to survive a winter?

Answer:

1. All of these bushes are local hybrids.

2. All of these local hybrids are rosa rogosa.

3. All rosa rogosa are very hardy bushes.

4. All very hardy bushes are plants that survive the harsh winters here.

5. So all of these bushes are plants that survive the harsh winters here.

The main conclusion is the last statement but how do we find the syllogisms that lead to this conclusion?

Rearrange them this way:

2. All of these local hybrids are rosa rogosa.

1. All of these bushes are local hybrids.

2a. First conclusion (not stated): All of these bushes are rosa rogosa. by AAA-1

Second syllogism:

3. All rosa rogosa are very hardy bushes.

2a. (not stated): All of these bushes are rosa rogosa.

3a. Second conclusion (not stated): All of these bushes are very hardy bushes.

Third syllogism:

4. All very hardy bushes are plants that survive the harsh winters here.

3a. (not stated): All of these bushes are very hardy bushes.

4a. Third conclusion: All of these bushes are plants that survive the harsh winters here.

Next lecture. 

This page is maintained by William S. Jamison. It was last updated August 14, 2012. All links on these pages are either to open source or public domain materials or they are marked with the appropriate copyright information. I frequently check the links I have made to other web sites but each source is responsible for their own content.