Fundamental Differences in the Philosophy of Sadra and Avicennan Philosophy about Motion

Since one of the explicit differences between Avicenna and Mulla Sadra ‘s philosophical thought based on the important issue of ‘ Motion specially ‘ Substantial Motion’ , and there ‘s complete difference in the debate , the author has tried to response the questions about the origins and theoretical basis of this difference and to find out which position and principal have been involved in this contrast.First part of the essay studies the difference between Avicenna and Mulla Sadra ‘s essential position through analytical comparison of ‘Motion Premise’ in the thought of these two well-known philosophers .1. Sadra’s perception of motion against Avicenna’s issues attitude and essence attitude. 2. Development of ‘ Motion’ discussion toward sensual affairs specially human soul.3. Change in the position of’ Motion Premise’ in philosophical natural sciences to common affairs.By analytical studying of the mentioned points specially with meditating in Avicenna’s objections on ‘Substantial Motion’, we conclude that the difference of these well-known philosophers in the premise of ‘Substantial Motion’ , originates in the most important philosophical position that is called ‘Principal of Existence’ or ‘Priority of Essence’ .On this basis of these facts and despite of all denials and doubts of some other thinkers in Avicennas’s ‘Principal of Essentialism’ thought, based on this philosophical analysis , it can be explicitly seen the consideration of ‘Essence Principal’ ,which at least can end the doubts about ‘ Motion Premise’