“Cursed be anyone who misleads a blind man on the road.” And all the people shall say, “Amen” (Deuteronomy 27:18).
In the Old Testament, there are two basic types of law: apodictic and casuistic. To say it more simply, there are general principles and specific cases. Apodictic laws are general laws, such as those given in the Ten Commandments—keep the Sabbath holy, do not steal, honor your father and mother, and the like. Casuistic laws are case laws, which deal with specifics. The prohibition of misleading the blind cited above is an example.
Both kinds of laws need to be interpreted. For instance, the apodictic command “keep the Sabbath holy” generated all kinds of interpretive questions in Jesus’ time. Is it OK to heal on the Sabbath? What about the disciples eating the grain as they were passing through a field in the Sabbath? What constitutes “work”? To use another example, does the command to honor your father and mother lay an obligation upon children to provide for their parents in old age? Jesus thought so, but apparently the Pharisees did not (Matthew 15). Both knew the commandment, but differed on how it was specifically to be applied. For these kinds of laws, we reason from the general to the specific.
Casuistic commands need to be interpreted as well, but they go in the opposite direction. Whereas the apodictic laws require reasoning from the general to the specific, casuistic laws require reasoning from the specific to the general. For instance, if it is forbidden to mislead the blind, is it OK to deceive the deaf? To put it that way makes plain the obvious. Although deceiving the deaf is not explicitly forbidden, it is implicitly forbidden in the protection given the blind (although see Leviticus 19:14). From the specific prohibition to misleading the blind we reason to the general prohibition of taking advantage of the vulnerable, whether they be the deaf, the lame, or the mentally ill. (To take it a step further, the law for the blind is another way of calling for the people of God to actively bless the vulnerable, to “defend the fatherless and plead for the widow”—Isaiah 1:17). Again, the law required the Israelite to install a parapet on his roof (Deut 22:8). Yet the Old Testament says nothing about banisters or cribs. The point of the parapet is to think ahead and order one’s home in such a way that people don’t experience unnecessary harm. The parapet leads to the crib (or the like).
The fact that both kinds of laws need to be interpreted does not mean that a law can mean what I want it to mean. Interpretations are not up for grabs. Yet, in cases where understanding exactly what a particular law means, perhaps the following will help: “So whatever you wish that others would do to you, do also to them, for this is the Law and the Prophets” (Matt 7:12).