Maturana, however, argued very vocally that this appropriation of autopoietic theory was conceptually unsound, as it presupposes the autonomy of communications from actual persons. That is, by describing social systems as operationally closed networks of communications, Luhmann (according to Maturana) ignores the fact that communications presuppose human communicators. Autopoiesis only applies to networks of processes that reproduce themselves, but communications are reproduced by humans. For this reason, the analogy from biology to sociology does not, in this case, hold. On the other hand, Luhmann explicitly stressed that he does not refer to a "society without humans", but to the fact that communication is autopoietic. Communication is made possible by human bodies and consciousness, but this does not make communication operationally open. To "participate" in communication, one must be able to render one's thoughts and perceptions into elements of communication. This can only ever occur as a communicative operation (thoughts and perceptions cannot be directly transmitted) and must therefore satisfy internal system conditions that are specific to communication: intelligibility, reaching an addressee and gaining acceptance.