Abstract

This paper proposes an epistemic logical framework for demanding knowing why in the natural sciences. Our focus is on the phenomena and their respective causal factors revealed by experiments. Two novel modalities \(\textsf{E}(\psi,\varphi )\) and \(\textsf {W}((\psi _1,\varphi _1)\bullet (\psi _2,\varphi _2)\bullet \cdots \bullet (\psi _n,\varphi _n))\) are introduced over models that deviate from the usual epistemic models by having both experimental evidence and the scientific theories, which is inspired by scientific practices. The modality \(\textsf{E}\) expresses scientists’ have (conclusive) experimental evidence indicating a dependence relation between the causal factor \(\psi \) and \(\varphi \). Based on the evidence, scientists often package some (perhaps seemingly unrelated) phenomena together, and the modality \(\textsf{W}\) captures scientists’ knowing why in their entirety, or having systematic knowledge-why of them, which amounts to having a _unified_ scientific theory of all these dependences. A sound and complete axiomatization is given, followed by a decidability result. Many notions of much philosophical interest are embodied in the present framework. We also draw several comparisons and connections with some existing relevant logical work.