Naturalistic Fallacy:

"In the view of the delicate relationship and . . . the complimentary relationship between rational reconstruction and empirical analysis, there is a danger of the naturalistic fallacy . . . Piaget tends to assimilate his approach to system theory. The concept of equilibrium, which points to a relative stability of problem-solving processes and is measured in terms of the internal criterion of the degree of reversibility, carries connotations of the successful adaptation of a self-maintaing system to a changing environment . . . . Every attempt to view that superiority of higher-level achievements, which are measured in terms of the validity of problem-solving attempts, in strictly functional terms places the specific achievement of cognitivist development in jeopardy. If what is true or morally right could be adequately analysed in terms of what is necessary for the maintenance of system boundaries, we would not need rational reconstruction.”

"Moral Consciousness and Communicative Action, pp. 34-35"

Idealistic Fallacy:

“As long as we cast the issue in transcendental terms, we have to distinguish sharply between the hermeneutic approach of a rational reconstruction of the structures of the lifeworld, which we undertake from the perspective of participants, and the observation-based causal analysis of how these structures naturally evolve. Only the idealistic fallacy of inferring an ontological difference between mind and body (or Being and beings) from a methodological distinction misleads us into locating the transcendental conditions of objective experience in a transmundane realm of the intelligible – or of the history of Being. Conversely, the naturalistic fallacy is but the other side of the same coin; without considering the aporia of self referentiality, and project them onto a scientifically objectified realm.”

"Truth and Justification, p. 28."