The decay of constitutions
In Books VIII and IX of the Republic, Plato gives the first great theory of political decline — an account of how the ideal constitution, once corrupted, degenerates through a sequence of worse and worse regimes. The platform reads it as the ancestor of every later cyclical theory of constitutional decay, including Polybius' and the modern theories of decline, and as one of the most penetrating things Plato wrote, all the more striking because the supposed champion of the ideal state turns his analytic power on the ways political orders fail.
The sequence
The platform reads Plato's sequence as a descent driven by the progressive dominance of the lower parts of the soul. From the ideal aristocracy (rule of the best, of reason) the city declines to timocracy (rule of the honour-loving, the spirited part — Plato's transparent portrait of Sparta); then to oligarchy (rule of the wealthy, of appetite organised around money); then to democracy (rule of the many, of appetite unleashed into unlimited freedom); and finally to tyranny (the rule of one lawless appetite over all), which Plato presents as the worst regime and the unhappiest condition of the soul. The platform reads each regime as paired with a corresponding type of person, so that the decay of constitutions is also the decay of character.
Democracy and tyranny
The platform reads Plato's most controversial claim as the link between democracy and tyranny. Democracy, in his analysis, prizes freedom above all and pushes it to excess, until every restraint — of law, of authority, of reason — is felt as oppression; the resulting disorder breeds a longing for a strong man to restore order, and the demagogue who exploits that longing becomes the tyrant. The platform reads this as a serious and uncomfortable argument — that unlimited freedom is unstable and tends to produce its opposite — that any defender of democracy must answer, taken up in Plato versus democracy.
Why it matters for Virtue & Power
Political degeneration is Plato's theory of decline and one of the platform's central treatments of how constitutions fail, to be read against Aristotle's empirical study of stasis and Polybius' cycle of constitutions. It connects the platform's reading of decline to the soul-and-city analogy at the heart of Plato's thought, and it is the dark counterpart to the ideal state.