Source : Webster's Revised Unabridged Dictionary (1913)

-ics \-ics\
   A suffix used in forming the names of certain sciences,
   systems, etc., as acoustics, mathematics, dynamics,
   statistics, politics, athletics.

   Note: The names sciences ending in ics, as mathematics,
         mechanics, metaphysics, optics, etc., are, with respect
         to their form, nouns in the plural number. The plural
         form was probably introduced to mark the complex nature
         of such sciences; and it may have been in imitation of
         the use of the Greek plurals ?, ?, ?, ?, etc., to
         designate parts of Aristotle's writings. Previously to
         the present century, nouns ending in ics were construed
         with a verb or a pronoun in the plural; but it is now
         generally considered preferable to treat them as
         singular. In Greman we have die Mathematik, die
         Mechanik, etc., and in French la metaphysique, la
         optique, etc., corresponding to our mathematics,
         mechanics, metaphysics, optics, etc.

               Mathematics have for their object the
               consideration of whatever is capable of being
               numbered or measured.              --John
                                                  Davidson.
         The citations subjoined will serve as examples of the
         best present usage.

               Ethics is the sciences of the laws which govern
               our actions as moral agents.       --Sir W.
                                                  Hamilton.

               All parts of knowledge have their origin in
               metaphysics, and finally, perhaps, revolve into
               it.                                --De Quincey.

               Mechanics, like pure mathematics, may be
               geometrical, or may be analytical; that is, it
               may treat space either by a direct consideration
               of its properties, or by a symbolical
               representation.                    --Whewell.