In general usage the terms speech and language are used interchangeably. Sematically one has to differentiate between speech and language. Language in its widest sense signifies the elaboration of thoughts and ideas. Language and thought are intimately related and mutually influence each other. Spoken words are arbitrary audible symbols, and propositional, that is, meaningful, speech may be regarded as verbal means of communication, a tool and a manifestation of language.
From a phylogenetic point of view, speech is the newest of man's skills. For its normal development one must have a normally functioning brain, adequate hearing, normal peripheral anatomical structures used in speech, and also a stimulating environment.
These peripheral structures are not special organs set aside solely for speech. Speech has arrogated to itself structures such as the mouth, lungs, and larynx that biologically perform more vital and quite different functions. The central nervous system acts as an integrator
KARLIN IW. Speech- and Language-Handicapped Children. AMA Am J Dis Child. 1958;95(4):370–376. doi:10.1001/archpedi.1958.02060050372005