The chapter (A Journey from Ontology towards Semantics) nuances an interwoven between the mind and the world from the spheres of ontology and epistemology. Descartes advocates the world-independent subsistence of the mind, while the double-edged nature of the Cartesian dualism nudges the nature of conscious mind that is causally interactive to the physical world. This doctrine of interaction as being ontological is closely tied to the epistemological hypothesis of cogito ergo sum, or ‘I think, therefore, I am’. The primal historical and conceptual moves from the epistemological analysis on the ontological problem of dualism is debunked when we trace back to the Post-Cartesian semantics basing on the analytic trend that introduces Descriptivism and the Causal theory of reference incoherently. This chapter shows how the theory of description (in the referential sense of Frege and Russell), self-knowledge and supervenience theory embed internalism as an exclusive thesis. Besides, the chapter pin down an antagonist theory called externalism that adheres to resolve the meaning and the content of our mental states or beliefs through causal chains (i.e., the causal theory of reference and socio-linguistic background). In short, this chapter attempt to comprehend the derivation of the enduring debate by scrutinizing what makes these theories (internalism and externalism) pervasive.