The judge and jurist Oliver Wendell Holmes Jr very aptly summed up the way such development works in his book The Common Law (1881). He noted:
The life of the law has not been logic: it has been experience. The felt necessities of the time, the prevalent moral and political theories, intuitions of public policy, avowed or unconscious, even the prejudices which judges share with their fellowmen, have had a good deal more to do than the syllogism in determining the rules by which men should be governed.
Source: P131, How the Law Works, Gary Slapper
I recognise the form of a syllogism from my math studies, but I'm guessing that the meaning here should be Definition 1.1? Yet I doubt this, because deduction doesn't always determine 'the rules ...'?