Edward Sapir 
Language, an Introduction to the Study of Speech [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Variability of language. Individual and dialectic variations. Time variation or drift. How dia lects arise. Linguistic stocks. Direction or slope of linguistic drift. Tendencies illustrated in an English sentence. Hesitations Of usage as symptomatic of the direction of drift. Leveling tendencies in English. Weakening of case elements. Tendency to fixed position in the sentence. Drift toward the invariable word.