Abstract with CitationsDominant models in cognitive science often assume that thought is continuously accessible and largely independent of physiological state (Friston, 2010; Evans & Stanovich, 2013). This paper challenges that assumption by introducing the Thought Generator–Thought Selector (TGTS) model: a biologically grounded theory of reflective cognition. TGTS distinguishes between reactive and reflective processes, proposing that the latter emerges only under specific physiological conditions governed by the interostate—a dynamic configuration of autonomic tone, inflammatory load, and sensory context (Thayer & Lane, 2000; Critchley & Harrison, 2013).In contrast to predictive coding frameworks such as the Free Energy Principle (Friston, 2010), which aim to minimise surprise through inference, TGTS conceptualises reflection as a biologically gated capacity that requires tolerating uncertainty. The model delineates a tripartite loop (Thought Generator → PreForm → Thought Selector), reconceptualises the amygdala as a systemic load detector (Arnsten, 2009), and reframes the prefrontal cortex as a gatekeeper of reflective access. TGTS offers four testable predictions linking cognition to heart rate variability (Thayer et al., 2012), cytokine profiles (Yirmiya & Goshen, 2011), neurotype-specific interostate patterns (Beauchaine, 2015), and entropy shifts during deliberation (Carhart-Harris et al., 2014).I first introduced this framework in The Jellyfish Mind (Rigley, 2025). Here, I expand on it to create a formal, testable model with implications for education, psychiatry, and sociopolitical cognition. Rather than presuming when thought occurs, TGTS asks: under what biological conditions is reflection even possible?