As I shall argue here, such ideal theories are methodologically problematic, and often lead philosophers to make serious mistakes, both at the theoretical level and at the level of evaluating particular concrete phenomena.

In many of the normative and evaluative branches of philosophy, philosophers have devised “ideal theories”—e.g. theories of what it is for an agent to be ideally virtuous, or of what it is for someone to think in an ideally rational way, or of what it is for a society to be an ideally just “well-ordered society”.

1. The methodological problem with ideal theory

An ideal F is one of the F's that are, in the relevant respect, the best possible F's. So, e.g., an ideally virtuous agent is one of the best (i.e. most virtuous) possible agents; to think in an ideally rational way is to think in the best (i.e. most rational) possible way; an ideally just society is one of the best (i.e. most just) possible societies.

So, to determine what an ideal F would be like, one has to answer two quite different questions:

What F’s are (in the relevant sense) possible?

What is it for one F to be (in the relevant respect) better than another?

Surely it is clear that these two questions belong to entirely different categories.

The first question is a modal question, about what is possible. Normally, the relevant sense of ‘possibility’ will make this an empirical question.

The second question is a normative or evaluative question, about what is better and what is worse in the relevant respect. Normally, the relevant sense of ‘better’ will make this a purely philosophical non-empirical question.

Clearly, it is dangerous to try to answer these two very different questions simultaneously. Unarticulated assumptions are liable to get smuggled in, without receiving adequate scrutiny.

It seems to be for this reason that it is almost never explained exactly what the relevant notion of ‘possibility’ is, and hardly ever argued that the ideal is indeed “possible” in that sense. (One honourable exception is Plato’s discussion of the sense in which the ideal state is “possible” in Republic 471c-473e.)

Instead, philosophers all too often shift back and forth: when they want to suggest that their “ideal” has some practical relevance, they strengthen the sense of ‘possibility’, in order to suggest that the ideal might be practically within reach; when they want to defend their ideal against objections, they weaken the sense of ‘possibility’, in order to suggest that the worlds where the ideal is realized are remote from our non-ideal actual world.





2. The theoretical mistakes of ideal theory

For evaluative and normative theorizing, what is most important is to articulate a plausible conception of what it is for one item in the relevant category to be better than another.

Ideal theorists may assume that their description of the ideal gives us an easy way of articulating such a conception of what it is for one item x to be better than another item y: x is better than y if and only if x is closer to the ideal than y.

However, simply describing an ideal does not determine a unique metric of closeness to the ideal. This point has recently come to be appreciated within formal epistemology: even if perfect probabilistic coherence is part of being ideally rational, there are many different ways of measuring how closely an incoherent set of beliefs approximates to being perfectly coherent. Further substantive discussion is required to see which is the appropriate metric. The same point surely applies to ideal theories of individual virtue or of social justice: just describing an ideally just society will not in itself give us a way of measuring how closely a less-than-perfectly just society approximates to ideal justice.

In this way, a focus on ideal theory has obscured one of the crucial tasks of evaluative and normative theories – viz. to articulate an account of degrees of justice, or degrees of virtue or of rationality (i.e. an account of what it is for x to be more just, or more virtuous or rational, than y).





3. Ideal theory’s mistaken evaluations of particular states of affairs

A focus on ideal theory can also lead to mistaken evaluations of particular states of affairs. Here there are mistakes both on the right (the mistakes of conservatives), and on the left (the mistakes of revolutionaries).

3a. Conservative mistakes

The wish to conceive of the ideal as practically relevant has often led theorists to misinterpret the actual world as closer to the ideal than it is. E.g. many mainstream American liberal political theorists seem to have been tempted to think that the US constitution is already close to the ideal. (There are clear signs, it seems to me, that Rawls thinks that the “basic structure” of the US political system is at least not too far away from the “realistic Utopia” that he refers to The Law of Peoples, p. 128.)

This has led to a tendency to take an excessively idealized view of the actual world, emphasizing how good things are in the world as it is actually is. Such an idealized view of the actual world can easily become part of a false ideology, informing pervasive mechanisms that disseminate propaganda, functioning to legitimize the position of those who are actually the most powerful and privileged.

3b. Revolutionary mistakes

Among those who focus on the ideal, those who see correctly how far the actual world falls short of the ideal may give in to a kind of rage or despair, in which all they can see is this gap between the actual and the ideal. In this state of mind, small improvements, which genuinely make the actual world better than it might otherwise have been, are not perceived as genuine improvements at all, because they do not achieve the ideal.

Those who fall into this mistake fail to see that sometimes “the perfect is the enemy of the good”. Unfortunately, we can be confident that we will never actually achieve the ideal. This should not lead us to despise smaller improvements that people do in fact achieve all the time.





4. The solution to these problems

The solution to these problems is simple. We need to separate the two questions that I distinguished in Section 1 above. The fundamental normative and evaluative questions are not about what is ideal, but about what is better and what is worse. Then there are also interpretive questions about what kind of ‘possibility’ is relevant to different normative issues. Finally, there are empirical issues about what is possible in the relevant sense.

If we separate the questions in this way, rather than focusing on the description of an ideal, then we will have some hope of avoiding all the mistakes that ideal theorists have been prone to.