 Whereas the signification of terms in spoken and written language is purely conventional and can be changed by mutual agreement (hence English speakers say ‘dog’ whereas in French it is chien), the signification of mental terms is established by nature, according to Ockham, and cannot be changed at will. Concepts, in other words, are natural signs: my concept of dog naturally signifies dogs. How this “natural signification” is to be accounted for in the final analysis for Ockham is not entirely clear, but it seems to be based both on the fact that simple concepts are normally caused within the mind by their objects (my simple concept of dog originated in me as an effect of my perceptual encounter with dogs), and on the fact that concepts are in some way “naturally similar” to their  objects.[23] 