Beginning in the mid-seventeenth century, thinkers in various disciplines evoked birds and other animals that appeared able to talk to make points about language use and human reason and identity. Talking birds initially allowed philosophers to draw parallels between language and the Cartesian model of human beings as both body and spirit, since language consisted of material sounds as vehicles for abstract ideas. By the eighteenth century the talking bird in literature had become a metaphor for a natural language that could express the truth in any and all circumstances. In later works of both literature and natural history, talking birds—and also monkeys—symbolized the point where thinking and material substances met. However, instead of offering a synthesis of those two substances, as the human does in Cartesian philosophy, talking animals highlighted a point of contention where thought and human identity were continuously and dynamically produced.