Tennessee Pattern Instructions (T.P.I).  Section 2.00.  

TN — CRIM. 2.03.  REASONABLE DOUBT

Reasonable doubt is that doubt engendered by an investigation of all the proof in the case and an inability, after such investigation, to let the mind rest easily as to the certainty of guilt.  Reasonable doubt does not mean a doubt that may arise from possibility.  Absolute certainty of guilt is not demanded by the law to convict of any criminal charge, but moral certainty is required, and this certainty is required as to every proposition of proof requisite to constitute the offense.