A want of acquaintance with the Gaelic language or with Highland feelings and modes of thought, is usually the cause of error. The writers think in English, and are not careful to eliminate from their statements thoughts derived from English or classical literature, or to keep from confusing with Celtic beliefs ideas derived from foreign sources, and from analogous creeds existing elsewhere. This gives an unconscious tinge to their statements, and (what is more to be regretted) sometimes makes them fill up with extraneous and foreign elements what seems to them gaps or blanks in beliefs they but imperfectly understand.