The epistemological problem of unity and its development in the philosophy of Bertrand Russell is the main subject of this essay. The first chapter is devoted to naïve realism developed by G. E. Moore and adopted by early Russell. I explain the notion of objective unity of proposition. The second chapter concerns Russell's departure from naïve realism and the multiple relation of judgment which Wittgenstein's criticism rendered as fatally unable to handle the problem of synthetic unity. The breakdown of this theory led Russell to naturalism, which is the topic of the last chapter. I pay special attention to the regressive argument proposed in slightly different versions by Moore, L. Wittgenstein and G. Ryle. Keywords realism, neutral monism, behaviorism, unity, consciousness

Logical pluralism from historical perspective - Abstract The plurality of logics is understood as a challenge to seek a deeper understanding of the na- ture and import of logic. Two basic approaches to demarcation of logic are considered, the model-theoretic and the proof-theoretic one. Investigation of the history which led to these two appraoches identifies the postion of logic in Kant's epistemology as crucial for the devel- opment. An analogical development from Kant's conception of geometry to the plurality of geometric theories leads to a holistic view both of geometry and of logic. It furthermore proves essential to understand the pragmatic import of logic. Given the problems tied to the attempts to demarcate logic, inferentialism and logical expressivism are arrived at as jointly provid- ing the most appropriate account. These approaches are developed into a conception which stresses, in line with the historical perspective of the work, the ability of logic to develop.