1. Friends and social networks

2. Strong and Weak Ties Strong ties: Intense attachment Often reinforced by other ties Weak ties: Acquaintances May link otherwise unconnected actors

3. Back to relationships and networks: What produces (solidary) groups? (1) similarity/selection (2) influence (3) (inter-)dependence

4. Start with an interesting theory: Balance theory simple theory of interaction generates ideal-types of social structures can be tested against data

5. Balance Theory A theory of action Basic idea is that persons seek to avoid tension or dissonance in their relations predicts that persons will change their relations in order to avoid dissonance Scope conditions Based on triads (groups of three) Assumes only positive (+) or negative (-) relations Assumes symmetry of relations Balance theory

6. Romeo Juliet Capulet - + + Unbalanced triad Romeo Juliet Capulet + + + Balanced Romeo Juliet Capulet - - + Balanced Romeo Juliet Capulet - + - Balanced Balance theory

7. Balance and Transitivity Balanced triads where no dissonance exists between members is called a transitive triad Technical measure of transitivity: Triads are transitive if the product of the sides is positive (+ x + x + = +; - x + x - = +) Triads are intransitive if the product of the sides is negative (+ x + x - = -) Balance theory

8. A D E + + + A D E - - + Transitive Triads A D E - - - A D E - + + Intransitive Triads Balance theory

9. ? W. Virginia Caucus: On the 2 nd round of balloting, McCain’s supporters voted for Huckabee

10. More on balance theory Some cultural rules: The friend of a friend is a friend An enemy of my friend is my enemy The friend of my enemy is my enemy The enemy of my enemy is my friend Balance theory

11. Can’t build a society from negative relations (things fall apart…) A D E - - -

12. DIABECGJFH But balance can produce groups Balance theory Trick: find the triads

13. Friends with Enemies with + - A D E + + + A B E + - - B I E - - + B D I A E - - - - + + + + Balance theory

14. Friends with Enemies with Balanced Opposition D A B E C G J F H Balance theory I

15. Balance Theory and the Formation of Groups In a world with only symmetric relations, we will find structures of balanced opposition (opposing solidary groups) “Us” and “them” Groups whose coherence comes from Similarities to those within; and Difference from those outside Real World examples of balanced opposition Interpersonal relations Ethnic conflict Global alliances Balance theory