Sign languages are not mime—in other words, signs are conventional, often arbitrary and do not necessarily have a visual relationship to their referent, much as most spoken language is not onomatopoeic. While iconicity is more systematic and widespread in sign languages than in spoken ones, the difference is not categorical. The visual modality allows the human preference for close connections between form and meaning, present but suppressed in spoken languages, to be more fully expressed. This does not mean that sign languages are a visual rendition of a spoken language. They have complex grammars of their own and can be used to discuss any topic, from the simple and concrete to the lofty and abstract.