I recently listened to a series of lectures on the subject of political philosophy by a Yale professor. They are fairly well done and I recommend them. But what struck me while listening to them is a common assumption found within all of the perspectives he mentioned. This assumption remains without argument even though it requires one.
He mentioned five theories. Marxism, social contract theory, utilitarianism, anti-enlightenment theories and democracy. With each of these he gave at least two different versions. Furthermore, he was careful to give the best version of each of these theories, indicate how they would respond to objections and why someone might believe each one of them. Finally, these theories cover all major theories of politics that exist today. So any commonality between these theories is a major assumption of our time.
Each of these five theories assume that content can be separated from form. There are a few ways this assumption shows up. The first is that descriptive politics can be separated from moral theory. This idea is that we can describe how politics works without using any moral claims. The second way this shows up is the idea that the freedom people exercise in political activities can be separated from moral theories and from human nature. There are a few ways this idea shows up. Governments are encouraged not to prefer a particular moral scheme, a particular religion or a particular theory of human nature. Instead, they are encouraged to allow everyone to follow their moral scheme, religion and theory of human nature so long as it does not interfere with anyone else. The final way this shows up is in the description of human rights. Human rights are not only understood in a secular fashion, but they are also separated from any theory of human nature, or the good that these rights aim at. This assumption that form can be separated from content in these three ways is what I will call The Liberal Assumption.
Nowhere is the lecture was the liberal assumption ever defended. In fact, it was not even mentioned. This assumption was simply brought in as a matter of unexamined moral theory. This assumption is rarely defended in the modern political theory simply because all of the modern political theories assume that it is at least mostly true. There are some few philosophers who disagree with this, but their objections are mostly ignored.
This assumption was soundly rejected by the major philosophers of the ancient and medieval period. Each of them placed a study of politics after that of ethics. Each of them used their metaphysics, including the metaphysics of human beings, in order to understand both ethics and politics. So the modern liberal assumption is new and therefore hardly something obvious or something that does not require argument.
Given all of this, the key question becomes obvious. Is the modern liberal assumption true or false? In order to answer that question, the liberal assumption must be divided into its three parts. The first part is the descriptive assumption, the second is the assumption of unbounded freedom and third is the assumption of ungrounded rights. It is also necessary to make sure that any examination of these assumptions is done while imputing the most plausible theory to it. If the liberal assumption is extremely common, then we must assume that it is well-grounded. If we can show that even the most well-grounded liberal assumption is false, then it is false generally. If we show that the most well-grounded liberal assumption is true, then we can examine exactly how well-grounded it must be in order to be true. On the other hand, if we use a less well-grounded assumption, then any conclusion will be less certain, and it will be easier to doubt it.
There is one further issue. We cannot assume any particular form in order to determine whether or not this assumption is true or false. For if this assumption is true given utilitarianism but not true given social contract theory, then this is an argument for utilitarianism. It would not be an argument against the liberal assumption. We cannot even limit the forms to the current contemporary theories. Perhaps some new form will be discovered in the future. So we cannot limit ourselves to a particular form or range of forms when discussing the truth of this assumption.