The works of Juan de la Cruz contain numerous passages dealing with human cognition, both ordinary and mystical. Beginning with his analysis of acts of knowledge common to all men, through the peculiar transformation of the rational powers undergone in the «dark night,» this study traces San Juan's examination of the mystic's knowledge in and through God. The sixteenth-century Spanish thinker stresses that conditionality is a fundamental character of all human knowledge, and brings to light a complex movement of contiguity between one and another mode of cognitive activity. Also discussed is the communication, through the instruments of prose and poetry, of the mystic's supereminent and therefore ineffable experience of knowledge and love. Relying upon Juan de la Cruz's own texts, it is shown how a relative communication can be effected despite the barriers separating mystical from ordinary cognition. The exploration highlights how San Juan turns for poetic symbols to the analogia entis, while at once basing his symbolism upon mysterious correlations between mystical, immediate cognition and ordinary acts of intellection mediated through sensation.