more from Oliver,A/Smiley,T

### Single Idea 14243

#### [catalogued under 4. Formal Logic / F. Set Theory ST / 3. Types of Set / c. Unit (Singleton) Sets]

Full Idea

Thomason says with no unit sets we couldn't call {1,2}∩{2,3} a set - but so what? Why shouldn't the intersection be the number 2? However, we then have to distinguish three different cases of intersection (common subset or member, or disjoint).

Gist of Idea

The unit set may be needed to express intersections that leave a single member

Source

Oliver,A/Smiley,T (What are Sets and What are they For? [2006], 2.2)

Book Reference

'Metaphysics (Philosophical Perspectives 20)', ed/tr. Hawthorne,John [Blackwell 2006], p.135