On a more serious note: cut up your Great Thingy into smaller independent ideas, and treat them as independent.
For instance a marxist would cut up Marx’s Great Thingy into a theory of value of labour, a theory of the political relations between classes, a theory of wages, a theory on the ultimate political state of mankind. Then each of them should be assessed independently, and the truth or falsity of one should not halo on the others. If we can do that, we should be safe from the spiral, as each theory is too narrow to start a spiral on its own.
Same thing for every other Great Thingy out there.
On a more serious note: cut up your Great Thingy into smaller independent ideas, and treat them as independent.
For instance a marxist would cut up Marx’s Great Thingy into a theory of value of labour, a theory of the political relations between classes, a theory of wages, a theory on the ultimate political state of mankind. Then each of them should be assessed independently, and the truth or falsity of one should not halo on the others. If we can do that, we should be safe from the spiral, as each theory is too narrow to start a spiral on its own.
Same thing for every other Great Thingy out there.