Bearing thus within my heart the love of truth as my only philosophy, and as my only method a clear and simple rule which dispensed with the need for vain and subtle arguments, I returned with the help of this rule to the examination of such knowledge as concerned myself; I was resolved to admit as self-evident all that I could not honestly refuse to believe, and to admit as true all that seemed to follow directly from this; all the rest I determined to leave undecided, neither accepting nor rejecting it, nor yet troubling myself to clear up difficulties which did not lead to any practical ends. But who am I? What right have I to decide? What is it that determines my judgments? If they are inevitable, if they are the results of the impressions I receive, I am wasting my strength in such inquiries; they would be made or not without any interference of mine. I must therefore first turn my eyes upon myself to acquaint myself with the instrument I desire to use, and to discover how far it is reliable. I exist, and I have senses through which I receive impressions. This is the first truth that strikes me and I am forced to accept it. Have I any independent knowledge of my existence, or am I only aware of it through my sensations? This is my first difficulty, and so far I cannot solve it. For I continually experience sensations, either directly or indirectly through memory, so how can I know if the feeling of self is something beyond these sensations or if it can exist independently of them? My sensations take place in myself, for they make me aware of my own existence; but their cause is outside me, for they affect me whether I have any reason for them or not, and they are produced or destroyed independently of me. So I clearly perceive that my sensation, which is within me, and its cause or its object, which is outside me, are different things. Thus, not only do I exist, but other entities exist also, that is to say, the objects of my sensations; and even if these objects are merely ideas, still these ideas are not me. But everything outside myself, everything which acts upon my senses, I call matter, and all the particles of matter which I suppose to be united into separate entities I call bodies. Thus all the disputes of the idealists and the realists have no meaning for me; their distinctions between the appearance and the reality of bodies are wholly fanciful. I am now as convinced of the existence of the universe as of my own. I next consider the objects of my sensations, and I find that I have the power of comparing them, so I perceive that I am endowed with an active force of which I was not previously aware.