From sources ranging from The Observer to medieval law and anthropology, Jacobs concluded that humans had developed two ways of gaining a living: 'taking' and 'trading', or 'conquest' and 'commerce'. She also found that each of these survival systems had a corresponding 'moral syndrome', built out of precept and tradition, modified over time. For example, it's hardly surprising to find that commerce thrives on a syndrome of honesty, competition, respect for contracts, initiative and enterprise, optimism, thrift, willingness to collaborate and agree, and avoidance of force.
The other syndrome, which Jacobs dubs the 'guardian' syndrome because it derives from territorial protection, by contrast emphasises loyalty, honour, tradition, prowess, exclusivity and the distribution of largesse. Trading is anathema to it. This syndrome governs the behaviour of governments and their bureaucratic and other agents, including police, armed forces and judges (also, incidentally, organised religion).
Three points are essential to understand how the syndromes work. The first is that they are practical and internally consistent, not arbitrary: they are 'what works', as evolved over time. Second, though mutually exclusive, they are also interdependent: commerce needs 'guardians' (the state) to establish and police the rules, guardians need commerce to provide energy and innovation, not to mention taxes. Finally, and crucially, they are systems. One characteristic of systems is that the parts work together and are self-reinforcing.
But by the same token it's impossible to change or remove individual elements without causing unintended consequences all along the chain. In this case, so sensitive to tampering are the syndromes that combinations of the two produce not a milder median, but what Jacobs calls 'monstrous hybrids', with the perverse property of turning virtues in one syndrome into vices in the other.
