Dysarthria is a disorder of speech whilst dysphasia is a disorder of language.
* Speech is the process of articulation and pronunciation. It involves the bulbar muscles and the physical ability to form words.
* Language is the process in which thoughts and ideas become spoken. It involves the selection of words to be spoken, called semantics and the formulation of appropriate sentences or phrases called syntax.
Strictly speaking, the words anarthria and aphasia mean a total absence of ability to form speech or language but they are often used when dysarthria and dysphasia would be more correct.
Dysphasia can be receptive or expressive. Receptive dysphasia is difficulty in comprehension whilst expressive dysphasia is difficulty in putting words together to make meaning. In reality there is usually considerable overlap of all these conditions but a person who has pure dysarthria without dysphasia would be able to read and write as normal and to make meaningful gesture provided that the necessary motor pathways are intact.
Inability to write is agraphia or dysgraphia if incomplete. Inability to manipulate numbers is acalculia or dyscalculia if incomplete. Difficulty reading is dyslexia.