 A central task of feminist philosophy of law is articulating what equality requires against this background of patriarchy; however, feminists take differing approaches to this problem. For liberal feminists, a primary task is achieving the principle of procedural equality articulated by Aristotle that like cases should be treated alike and different cases differently in proportion to their differences. For other feminists, this focus on procedural justice raises the question of whether there are differences between men and women that the law may justifiably take into account. For many centuries men and women have been viewed as significantly different, and since they are different it has been thought appropriate and justified to treat them differently in law. Indeed, one of the reasons for the entrenchment of sexual inequality is precisely the observation that some differences between men and women are real: only women can become pregnant and bear children. Historically, feminists contend in a variety of ways, such differences were greatly exaggerated, as was their significance and the extent to which they could be attributed to biology rather than being socially constructed.