Sum translated as "I exist" (per various Latin to English dictionaries) presents a much larger and clearer meaning to the phrase.
[6]: 6 Mario Bunge argues that methodological skepticism presupposes that scientific theories and methods satisfy certain philosophical requirements: idealism, materialism, realism, rationalism, empiricism, and systemics, that the data and hypotheses of science constitute a system.
Consider Descartes' opening lines of the Meditations: Several years have now elapsed since I first became aware that I had accepted, even from my youth, many false opinions for true, and that consequently what I afterward based on such principles was highly doubtful; and from that time I was convinced of the necessity of undertaking once in my life to rid myself of all the opinions I had adopted, and of commencing anew the work of building from the foundation...—Descartes, Meditation I, 1641René Descartes, the originator of Cartesian doubt, put all beliefs, ideas, thoughts, and matter in doubt.
Descartes, knowing that the context of our dreams, while possibly unbelievable, are often lifelike, hypothesized that humans can only believe that they are awake.
"—Descartes: Selected Philosophical Writings[13]: 122 Descartes reasoned that our very own experience may very well be controlled by an evil demon of sorts.
[1] As a result of this doubt, sometimes termed the Malicious Demon Hypothesis, Descartes found that he was unable to trust even the simplest of his perceptions.
[15]: 66 In Meditation I, Descartes stated that if one were mad, even briefly, the insanity might have driven man into believing that what we thought was true could be merely our minds deceiving us.
He also stated that there could be 'some malicious, powerful, cunning demon' that had deceived us, preventing us from judging correctly.
[18]: 83 Indeed, Descartes' attempt to apply the method of doubt to the existence of himself spawned the proof of his famous saying, "Cogito, ergo sum" (I think, therefore I am).