Pharmaceutical knowledge is distributed across chemical, biological, preclinical, clinical, safety, formulation, and regulatory-adjacent data environments that encode different objects, relations, contexts, and evidentiary standards. Although contemporary computational methods can connect parts of this landscape, predictive performance on an isolated task does not establish that the underlying representation is scientifically coherent, evidentially traceable, or suitable for pharmaceutical reasoning. This article proposes a unified pharmaceutical reasoning space as an original knowledge-representation architecture for organizing molecules and drug products, targets, pathways, phenotypes, diseases, and therapeutic evidence within one context-sensitive semantic substrate. The approach is architectural rather than empirical: it synthesizes representational requirements from pharmaceutical data integration, biomedical knowledge graphs, curated molecular resources, pathway knowledgebases, phenotype ontologies, and evidence-aware reasoning. The central contribution is the context-qualified, evidence-bearing assertion, defined as a typed relation between canonical entities that retains provenance, evidence class, biological and experimental context, temporal status, uncertainty, and contradiction without collapsing these dimensions into a single score. The architecture separates source ingestion, semantic representation, reasoning services, validation, and decision use so that graph connectivity, embedding proximity, or ranking performance cannot silently become claims of mechanism, causality, clinical utility, or regulatory acceptability. Its principal limitations are dependence on source quality, incomplete ontological alignment, unresolved contextual gaps, and the absence of empirical validation. The proposed reasoning space may nevertheless provide a disciplined basis for integrating heterogeneous pharmaceutical evidence, comparing competing explanations, and designing future evaluation programs across discovery, safety, and repurposing.