A quote from Frederik Stjernfelt, Natural Propositions: The Actuality of Peirce’s Doctrine of Dicisigns
p. 107 “If no universals refer to real structure, then all universals are but labels invented by the human mind. If propositions do not exist in reality they, as well, must be creations of the human mind. … The implication is that on the one hand, we get an emaciated natural world consisting of isolated particulars only, bereft of any generality. On the other hand, in the very same universe, one particular, strange kind of object is supposed to stand out – the mind – which alone has the ability to create general objects and syntheses, namely those labels assumed identical from one use to the next, the names of the nominalists. So ontological stinginess as to the natural world automatically seems to imply the abnormal and extreme ontological overpopulation of the human psyche – otherwise assumed to form part of the very same natural world. Philosophers may be satisfied with bracketing that psyche, leaving the problem to psychologists – but that only leaves the road open for exactly psychologism, the tendency to locate ontological and logical structure in the mind of the beholder and take psychology to be the science studying them. So nominalism and psychologism often, if not always, go together.”