Allegro is a term which refers to music and which means <span>you should play a piece at a quick tempo ad the word means happy. There are many Italian terms which are used in music to explain or to show the speed or tempo of the music. Most of the terms in music are Italian because many important composers of early period were Italian.</span>
Sound is often used to mean sure, or clear. Sound reasoning is simply reasoning that makes sense, and follows some sort of logic. Sound reasoning means logical reasoning.
