infringing on people’s economic activity and thus that justice must be silent about any social and economic inequalities. From the opposite extreme, a radical egalitarian theory of justice will deny that justice can ever countenance inequalities of any kind and thus that justice will not permit any social or economic inequalities, even if they are to the benefit of the least advantaged group. Less extreme, but still differing from Rawls’ theory, the utilitarian theory of justice would allow for justice to regulate social and economic inequalities but would do so with an eye to maximizing utility instead of benefiting the least advantaged group. Each of these is a theory of justice—an explanation of justice by means of a system of thought about justice. Each in turn will issue a different answer to and explanation of our question about social and economic inequalities. The first virtue of theories, systems of thought, is truth or some other kind of epistemic goodness. Which of these competing theories is true or epistemically good?
Methods of Theory Evaluation
Once we realize that we cannot simply divine which of these competing theories is true by direct assessment, it is clear that we need methods for evaluating theories. This is an important lesson at the root of all theorizing: the first virtue of theories is truth, yes, but given that we do not have direct, unmediated access to the truth of theories, we need some medium, some indirect means for assessing the truth of theories. Methods of theory evaluation are precisely such indirect means of truth assessment. Now, this can be fairly straightforward. Perhaps, the principal method of theory evaluation we have at our disposal is fit with the data or fit with other truths. This method says that we can assess the truth of theories by how well they fit with other things we know to be true. An example above illustrates this well, the question: “Did Colonel Mustard kill Mr. Boddy?” We want to know the answer to this question; to fully satisfy our questioning, we’ll need an explanation of the death of Mr. Boddy, which would be provided by a theory of the death. Let’s stipulate that we have several pieces of data. We know that it is true that: (1) Mr. Boddy was found, dead, in the library. (2) Colonel Mustard was found in the library holding a bloody candlestick. And (3) Colonel Mustard stands to inherit Mr. Boddy’s estate. Now we can ask: What is the answer to our question, what explains the death of Mr. Boddy? The following theory obviously stands out as the best theory, the true theory: “Colonel Mustard did kill Mr. Boddy. He killed him in the library with a candlestick in order to inherit the estate.” This theory answers our question and we know it is the true theory because it obviously fits best with the data. There are competing theories: “Colonel Mustard did not kill Mr. Boddy. Instead, Professor Plum killed Mr. Boddy in the drawing room with a wrench in a fit of rage over a failed business deal.” This theory is an answer to and explanation of our question, it is a competitor with the theory that says Colonel Mustard did it. It is possible that this latter theory is the true theory of the death of Mr. Boddy. But this theory is obviously weaker than the Colonel Mustard theory; we have every reason to believe that the Colonel Mustard theory is the true theory because it succeeds so much on the rubric of fit with the data. Notice then that the method which looks for fit with the data is still an indirect means for evaluating the truth of theories. We get at the truth of the theory in question by looking to another property—another property besides truth—that this theory possesses. For this method, the property is how well the theory fits with other truths. Truth is still bound up in this method, but it is not a method for direct assessment of the truth of theories.
There is another straightforward method of theory evaluation closely related to truth: the principle of noncontradiction. We know that contradictions are false. Thus, we have another tool for evaluating the truth of theories: if the theory includes or entails a contradiction, then we know that that theory is false. Another of the examples above illustrates this well, the question: “Do heavier objects fall faster than lighter objects?” We can answer this question by means of the fit with data method of theory evaluation. We can explain, “No, heavier objects do not fall faster than lighter objects because the principle that says that they do does not fit with observed truths, namely, the observed fact that two objects of different weights fall at the same speed.” Galileo, of course, famously conducted such experiments. But Galileo also saw that we don’t even need to do such experiments to explain our answer to the question. We can use the method of noncontradiction to answer our question in the negative. To do this, we must see that the positive answer (“Heavier objects do fall faster”) entails a contradiction. Why? Run this thought-experiment: Object A is heavier than Object B. By the theory in question (“Heavier objects do fall faster”), Object A will fall faster than Object B. Now join together Object A and Object B by a rope to form the composite Object C. Object C weighs the sum of Object A and Object B (plus the weight of the rope) and so is heaviest and should fall fastest of all. But we also said that Object B falls slower than Object A, so Object B should act as a drag on Object A and thus make Object C fall slower than the unencumbered Object A. Thus, Object C falls both faster and slower than Object A. This is a contradiction. Contradictions are necessarily false. Thus, the theory that entails the contradiction is also false. Thus, we’ve discovered something about the truth status of the theories in question. Specifically, we’ve discovered that one of the two competing theories to answer our question is false. And since there are only two competing theories, which exhaust logical space, we can conclude that the other theory (“Heavier objects do not fall faster”) is true. Thus, we’ve discovered the truth of a theory, which was our goal.
This can seem closer to a means of direct assessment of the truth of a theory, but it is not. This is still a method, a mediated means for evaluating the truth of theories. We do not directly assess the truth of the theories in question, rather we assess a modal property of that theory—impossibility. We know that this modal property is connected to a truth property and thus we can assess the truth of a theory by means of this modal property. But we are still evaluating the truth of the theory by means of another property of that theory. And in the case of the method of theory evaluation that uses the principle of noncontradiction, there is another way in which it is indirect. This method is purely negative: the modal property of impossibility is connected with the truth value falsity. We of course don’t just want to know which theories are false, we want to know which theories are true. In the falling object case above, this worked because there were only two theories that exhausted logical space. Finding that one was false was sufficient to find the other true. But this will not always be the case. If there are multiple competing theories, more than one of which does not entail a contradiction, then the method of theory evaluation which uses the principle of noncontradiction will not be sufficient to evaluate the truth of the competing theories.
We can overcome this negative problem by pointing to yet a third method of theory evaluation, the inverse of the principle of noncontradiction: the principle of necessity. We know that things that are necessary are true, and thus to find that a theory is necessary (or entailed by something necessary) will be to find that it is true. This has been attempted in the history of philosophy and is well illustrated by another of the example questions above: “Does God exist?” Traditional arguments for God’s existence have often tried to show that God’s existence is necessary or that it follows from something necessary. If this is successful, this would indeed be a method for evaluating as true the theory that explains that God exists. But note that this is still an indirect method for evaluating the truth of the “God exists” theory, in the same modal way as with the principle of noncontradiction: we find that that theory has a modal property—necessity—and we know that that modal property is connected to the truth value true. Thus, discovering necessity in a theory is a good method for evaluating the truth of that theory. The trick of course is that necessity is a difficult concept and all the pudding is in figuring out whether God’s existence is necessary or is entailed by something necessary. The person who thinks the “God exists” theory is false does not deny that looking for necessity is a good method for evaluating the truth of theories; this person denies that the theory exhibits such necessity. This method thus still involves an indirectness: it evaluates the truth of a theory by looking to whether that theory possesses another property: necessity. So, both the methods that use the principle of noncontradiction and the principle of necessity are still indirect methods of evaluating the truth of a theory: they do not directly assess the truth of a theory, rather they assess a modal property which we know to
