Source : Webster's Revised Unabridged Dictionary (1913)

Theory \The"o*ry\, n.; pl. {Theories}. [F. th['e]orie, L.
   theoria, Gr. ? a beholding, spectacle, contemplation,
   speculation, fr. ? a spectator, ? to see, view. See
   {Theater}.]
   1. A doctrine, or scheme of things, which terminates in
      speculation or contemplation, without a view to practice;
      hypothesis; speculation.

   Note: ``This word is employed by English writers in a very
         loose and improper sense. It is with them usually
         convertible into hypothesis, and hypothesis is commonly
         used as another term for conjecture. The terms theory
         and theoretical are properly used in opposition to the
         terms practice and practical. In this sense, they were
         exclusively employed by the ancients; and in this
         sense, they are almost exclusively employed by the
         Continental philosophers.'' --Sir W. Hamilton.

   2. An exposition of the general or abstract principles of any
      science; as, the theory of music.

   3. The science, as distinguished from the art; as, the theory
      and practice of medicine.

   4. The philosophical explanation of phenomena, either
      physical or moral; as, Lavoisier's theory of combustion;
      Adam Smith's theory of moral sentiments.

   {Atomic theory}, {Binary theory}, etc. See under {Atomic},
      {Binary}, etc.

   Syn: Hypothesis, speculation.

   Usage: {Theory}, {Hypothesis}. A theory is a scheme of the
          relations subsisting between the parts of a systematic
          whole; an hypothesis is a tentative conjecture
          respecting a cause of phenomena.

Binary \Bi"na*ry\, a. [L. binarius, fr. bini two by two, two at
   a time, fr. root of bis twice; akin to E. two: cf. F.
   binaire.]
   Compounded or consisting of two things or parts;
   characterized by two (things).

   {Binary arithmetic}, that in which numbers are expressed
      according to the binary scale, or in which two figures
      only, 0 and 1, are used, in lieu of ten; the cipher
      multiplying everything by two, as in common arithmetic by
      ten. Thus, 1 is one; 10 is two; 11 is three; 100 is four,
      etc. --Davies & Peck.

   {Binary compound} (Chem.), a compound of two elements, or of
      an element and a compound performing the function of an
      element, or of two compounds performing the function of
      elements.

   {Binary logarithms}, a system of logarithms devised by Euler
      for facilitating musical calculations, in which 1 is the
      logarithm of 2, instead of 10, as in the common
      logarithms, and the modulus 1.442695 instead of .43429448.
      

   {Binary measure} (Mus.), measure divisible by two or four;
      common time.

   {Binary nomenclature} (Nat. Hist.), nomenclature in which the
      names designate both genus and species.

   {Binary scale} (Arith.), a uniform scale of notation whose
      ratio is two.

   {Binary star} (Astron.), a double star whose members have a
      revolution round their common center of gravity.

   {Binary theory} (Chem.), the theory that all chemical
      compounds consist of two constituents of opposite and
      unlike qualities.