The integration of artificial intelligence (AI) into materials science has substantially accelerated property prediction and materials screening. Yet, the predominance of data-driven correlations has exposed a persistent epistemic gap between predictive success and the derivation of interpretable, generalizable design rules. This conceptual manuscript develops a theoretical framework for knowledge extraction in materials AI that explicitly addresses this gap by reframing the transition from correlations to design rules as a staged epistemic process rather than a by-product of model performance. Drawing on literature in materials informatics, data bias, and philosophy of science, the framework organizes knowledge extraction into four interconnected stages—Correlation Mapping, Bias Interrogation, Value Integration, and Rule Synthesis—linked through continuous epistemic validation. The model foregrounds epistemic agency, requiring explicit scrutiny of assumptions, biases, and value commitments before causal inference. Six propositions articulate the conditions under which AI-derived correlations may legitimately support prescriptive design claims, emphasizing reflexive feedback and epistemic governance. By conceptualizing knowledge extraction as a norm-governed process of justification, this work provides a theoretical scaffold for transforming AI outputs into scientifically defensible design rules, contributing to a more reliable and responsible epistemology of materials discovery.