In terms of philosophical certainty: The entire realm of my experience of existence is limited by my capacity to perceive and to consider. I know some form of 'I' the philosopher 'exists' in some form. I perceive and consider things, though this by no means suggests those things exist independent of me and my experience. I also acknowledge my experience of existence can be effected by things I am (or was) not aware of.
I can for example trip over something I was not aware was behind me; I can unknowingly view a room purely through a lens in the air (which alters how I perceive the next room), it would be a vastly different experience of that other room through that lens as opposed to without (though the lens itself might be a component of 'I', subconsciously inserted into my experience of existence).
I can recognise by implication that the conscious 'knowledge' currently available to 'I', might be imperfect; to be able to recognise incongruence between my experiences and my perceived 'knowledge'. It is therefore possible for me to 'learn', to gain altered or additional access to information, 'I' can come to believe something I did not before, or to understand it in a different way. This suggests two things: firstly that the scope of 'I' can change to incorporate new understandings and secondly that all else that can be perceived or considered must at the absolute least be available to 'I' for it to be processed, thus it must exist at least as some component of 'I' (though it still does not imply 'not I' exists in a similar manner as 'I').
An imperfect I exists in a state of change; anything I perceive or conceive exists - at least as part of I. Of this I am philosophically 'certain'.
In terms of pragmatic acceptance: The only thing I pragmatically accept is the natural scope of existence; things I can and cannot perceive yet are subject to a system of laws and constraints, the (imperfectly understood) laws of existence, be it logic, mathematics etc; things that can be reasoned to fit these laws and to be predicted and repeatedly demonstrated to show the imperfect knowledge we have is 'reasonable' in it's ability to predict reality even if not perfect - all of it I pragmatically accept as 'real' components of existence. All the while acknowledging 'I' and other cognizant entities exist with relation to being housed in natural containers, that each cognizant entity might be similar to me in that it has imperfect knowledge and does it's best to understand reality. Because of this some people attempt to learn things and to refine understanding of reality, while others attempt to assert things and to redefine reality to fit.