The interaction decoder utilized in prevalent Transformer-based HOI detectors typically accepts pre-composed human-object pairs as inputs. Though achieving remarkable performance, such a paradigm lacks feasibility and cannot explore novel combinations over entities during decoding. We present LogicHOI, a new HOI detector that leverages neural-logic reasoning and Transformer to infer feasible interactions between. entities. Specifically, we modify. self-attention mechanism in the vanilla Transformer, enabling it to reason over the ⟨ human, action, object ⟩ triplet and constitute novel interactions. Meanwhile, such a reasoning process is guided by two crucial properties for understanding HOI: affordances (the potential actions an object can facilitate) and proxemics (the spatial relations between humans and objects). We formulate these two properties in first-order logic and ground them into continuous space to constrain the learning process of our approach, leading to improved performance and zero-shot generalization capabilities. We evaluate L OGIC HOI on V-COCO and HICO-DET under both normal and zero-shot setups, achieving significant improvements over existing methods.