In con­trast to tra­di­tio­nal phi­lo­so­phy, Haber­mas does not view his ‘post­me­ta­phy­si­cal thought’ as a con­cep­ti­on of rea­li­ty that claims to be true. Actual­ly, howe­ver, his ‘post­me­ta­phy­si­cal thought’ is a meta­phy­si­cal dua­lism, which stands in oppo­si­ti­on to the meta­phy­si­cal natu­ra­lism pro­po­sed by other con­tem­po­ra­ry phi­lo­so­phers. In a spe­ci­fic way, he draws upon the Kan­ti­an idea of the con­sti­tu­ti­ve func­tion of reason. He holds, as other con­s­truc­ti­vists, an idea­li­stic meta­phy­sics that leads him to the con­s­truc­tion of an epis­te­mic dua­lism, con­tras­ting the objec­ti­ve world of the natu­ral sci­en­ces with the ‘Lebens­welt’. It turns out that he is unable to sol­ve the pro­blems con­nec­ted with this view. Meta­phy­si­cal rea­lism, which avo­ids the­se pro­blems, is rejec­ted by him. His ‘post­me­ta­phy­si­cal thought’, Haber­mas tells us, does not pre­su­me to deci­de what is reasonable or not in reli­gious tea­chings. The core of reli­gious expe­ri­ence, he sug­gests, is ‘opaque’ and the­r­e­fo­re immu­ne to cri­ti­cism. Faith and know­ledge are, as it seems, incom­men­sura­ble, so that a reasonable cri­tique of reli­gi­on is impos­si­ble. Thus, he cons­ents to an arbi­tra­ry rest­ric­tion of the use of reason, as pro­po­sed also by Joseph Ratzinger.