Carneades: *
Spengler is making a subtle point. Skeptics argued against the Stoics & called into question the possibility of knowledge. The Stoics maintained it was possible to achieve wisdom free of false belief. All true judgments are instances of knowledge based on an unshakable grasp of the truth. Knowledge of this kind was possible because there exists cognitive impressions which function as the criterion of truth. As the criterion of truth, cognitive impressions are the ultimate basis of all knowledge. Carneades pointed to dreams, madness, optical illusions & divinely inspired visions & argued that the special character allegedly proper to cognitive impressions was not peculiar to only these impressions but could also be found in false impressions If cognitive impressions arise, even if true they will be indistinguishable from false impressions & thus cannot serve as a criterion for truth. And if one accepts the Stoic assumptions regarding truth, it follows nothing can be known. Spengler is making the point that the skeptics did not accept Nature laws or the absolute necessity of cause-effect. That too might be a false cognitive impression.