Our thesis in this book is simple: choice often requires making trade-offs between various goals. In other words, individuals and groups have various ends and purposes they seek to achieve. For example, from its inception, the founding of the modern federal government of the United States was predicated on the need and desire to aggregate multiple goals:

Of course, it is rare that (say) establishing justice and securing the blessings of liberty will be simultaneously and maximally furthered by the same course of action. Unless such a fortuity occurs, governance – choosing and implementing public policies – requires making trade-offs between these goals. Regardless of whether these trade-offs are explicit or implicit, we have argued that aggregating goals is a ubiquitous characteristic of governance.

Aggregation is the heart of social choice theory. In Part I of the book, we have presented and discussed several seminal results from social choice theory. These results have been misinterpreted by scholars in various ways. The most important misconception about these results, in our minds, is an implicit presumption that the central results of social choice – Arrow’s Theorem and the Gibbard-Satterthwaite Theorem – apply only to methods of aggregating individual preferences.