Mo. Const. art. I, § 22(a)

That the right of trial by jury as heretofore enjoyed shall remain inviolate; provided that a jury for the trial of criminal and civil cases in courts not of record may consist of less than twelve citizens as may be prescribed by law, and a two-thirds majority of such number concurring may render a verdict in all civil cases; that in all civil cases in courts of record, three-fourths of the members of the jury concurring may render a verdict; and that in every criminal case any defendant may, with the assent of the court, waive a jury trial and submit the trial of such case to the court, whose finding shall have the force and effect of a verdict of a jury. [Effective - 27 Feb 1945 , see footnote]