This interdisciplinary paper reframes logic as a neurocognitive function by integrating philosophical critiques (Hume, Nietzsche) with psychological theories of coherence and neuroscientific models of large-scale brain networks (Salience, Central Executive, Default Mode). Using a theoretical integrative review approach, the paper combines philosophical arguments about epistemic circularity and self-reference with psychological evidence on cognitive dissonance, confirmation bias, and dual-process theory to demonstrate how logical reasoning primarily serves cognitive coherence management. Neuroscientific findings on network dynamics and neural connectivity mechanisms ground how pattern-completion, salience detection, and executive control instantiate reasoning processes. Rather than treating logic as a metaphysical route to mind-independent truth, the paper argues it operates as a biologically grounded, adaptive cognitive tool whose authority is pragmatic-functional: it supports intrapsychic coherence, predictive ability, and social communication. Together, these perspectives indicate that logic's normative force is rooted in embodied, evolutionary, and networked brain mechanisms rather than abstract metaphysical necessity. Implications for applied psychology are far-reaching, including mental health applications through clinical investigations of network disruptions (e.g., OCD, schizophrenia, autism), educational innovations to foster critical reasoning while accounting for cognitive constraints, and cross-cultural studies of reasoning development. This synthesis bridges conceptual analysis and empirical research, proposing a new framework for interdisciplinary work on the biological bases of cognition, social communication and cohesion.