The objective reality of ideas play san important role in the cartesian system, for upon it rests the whole force of his demonstration of the existence of God. Ex hoc (idea entis summe perfecti) enim uno tot avis demonstrationis meae dependet. Not only does the demonstration of God's existence take its point of departure from the objective reality of ideas, but it is an axiom that the knowledge which we have of all things, sensible and insensible, rests on the objective reality of our ideas and on the application to it of the causal axiom. Omnia enim diligentissime circumspexi, et nullum aliud argumentum potui hactenus reperire. Important as this position is in the cartesian system for the reason that the actual existence of beings other than the thinking substance can be demonstrated only by beginning with the objective reality of ideas, still this docritrine was the cause of surprise and of many objections from his contemporaries. Descartes admits that the author of the first set of objections puts in brief compass his own argument for proving the actual existence of God, and, having indicated his assent to that which he thinks is clearly enough demonstrated, comes to the crux of that which is difficult in the demonstration.