The first words uttered in my first lecture in applied welfare economics by Bob Rutherford were ‘this course starts with an explicit political position – that of liberalism’. I never forgot that.
This leads us to Robert and Zeckhauser’s taxonomy of disagreement:
Positive disagreements can be over questions of:
1. Scope: what elements of the world one is trying to understand?
2. Model: what mechanisms explain the behaviour of the world?
3. Estimate: what estimates of the model’s parameters are thought to obtain in particular contexts?
Values disagreements can be over questions of:
1. Standing: who counts?
2. Criteria: what counts?
3. Weights: how much different individuals and criteria count?
Any positive analysis tends to include elements of scope, model, and estimation, though often these elements intertwine; they frequently feature in debates in an implicit or undifferentiated manner. Likewise, normative analysis will also include elements of standing, criteria, and weights, whether or not these distinctions are recognised.
The origin of political disagreement is a broad church indeed in a liberal democracy. Those you disagree with are not evil, they just disagree with you. As Karl Popper observed:
There are many difficulties impeding the rapid spread of reasonableness. One of the main difficulties is that it always takes two to make a discussion reasonable. Each of the parties must be ready to learn from the other.