Jacob Grimm, following up the suggestion of a Danish Scholar, Rask, formulated explanation which accounted for the correspondences between certain consonants in Germanic language and those found in Sanskrit, Greek, and Latin. According to Grimm, the original voiceless stops (p, t, k) were changed to spirants (ph, th, h). So, Latin (tres) became English (three), Latin (centum) was English (hundred). Similar, correspondences can be traced out for certain other groups of consonants and the formulation of these correspondences is known as Grimm’s Law.
The certain exception to Grimm’s Law was explained by Karl Verner and other. It was noted that between such a pair of words as Latin centum and English hundred, the correspondence between c and h was according to rule, but that between the t and d was not. The ‘t’ in the Latin should have been hunthed.
Such an exception to Grimm’s Law was further explained under a separated theory which is known as “Stress Shift” or Verner’s Law. According to it, the Indo-Aryan p, t, h immediately follow the Law accent in a word: it shifts regularly in Law German English to f, th, h. But, if p, t, k is preceded by an accented syllable then they became as it were by taking a double sound shifting to b, d, g. The English Father, Mother, and Brother have Teutonic equivalents as gader, moder and broder which the true Aryan types are Pater, Mater, and Frater. The last syllables of these show ‘t’ shifting to ‘d’ and it undertakes a double consonantal shift.
Verner has demonstrated that the factor which causes these variations is ‘accent’ Verner’s Law in fact, studied the shifting of the place of the accent. Verner held the opinion that Teutonic “German or English” accent was off on unaccented on the former syllable kept its “th” unchanged, but the Teutonic “father” accented (as in the earliest period) on the latter syllable further changed ‘th’ to ‘d’ and ‘father’ becomes ‘fader’.
Verner’s Law explains a large number of anomalies that had frequently been noticed and had never before received any satisfactory explanation. It is sufficient to say that Verner’s Law explains so many cases in which Grimm’s Law fails. Verner’s theory of Stress shift has left its mark on the structure of the language and has influenced it more than any other phonetic changes.