AQuantitative or tested: Turchin, Kondratiev (Grinin & Korotayev), Modelski, debt waves, inequality and polarization series.
BScholarly-interpretive: Perez, Dalio, Arrighi, Skowronek, Goldstone, Fischer, Reinhart & Rogoff.
CPopular heuristic: Strauss–Howe, Glubb, Tickle, Harrison, Elliott, Kurzweil.
PPhilosophical lens with no clock: Polybius, Spengler, Toynbee, Sorokin.
XPhysical, no social link shown: solar cycles, precession.
SEsoteric or astrological: never evidence.