You might think you can be 100% sure of your existence following the line of Descartes' cogito ergo sum, "I think therefore I am". However in Being & Time (116) Heidegger dismantles the I by observing that any functional mind is a social development. At least we can be 100% sure that there is thought: that thought exists.
The word 'I' is to be understood only in the sense of a non-committal
formal indicator, indicating something which may perhaps reveal itself as its 'opposite' in some particular phenomenal context of
Being. In that case, the 'not-I' is by no means tantamount to an
entity which essentially lacks 'I-hood' ["Ichheit"], but is rather a
definite kind of Being which the 'I' itself possesses, such as having
lost itself [Selbstverlorenheit].
Yet even the positive Interpretation of Dasein which we have so far
given, already forbids us to start with the formal givenness of the
"I", if our purpose is to answer the question of the "who" in a way
which is phenomenally adequate. In clarifying Being-in-the-world we
have shown that a bare subject without a world never 'is' proximally,
nor is it ever given. And so in the end an isolated "I" without Others
is just as far from being proximally given. If, however, 'the Others'
already are there with us [mit da sind] in Being-in-the-world, and
if this is ascertained phenomenally, even this should not mislead us
into supposing that the ontological structure of what is thus
'given' is obvious, requiring no investigation. Our task is to make
visible phenomenally the species to which this Dasein-with in closest
everydayness belongs, and to Interpret it in a way which is
As for everything that appears for the mind to think on . . .
In the immediate circle of beings we believe ourselves to be at home.
The being is familiar, reliable, ordinary. Nonetheless, the clearing
is pervaded by a constant concealment in the twofold form of refusal
and obstructing. Fundamentally, the ordinary is not ordinary; it is
extra-ordinary, uncanny [un-geheuer]. The essence of truth, i.e.,
unconcealment, is ruled throughout by a denial. This denial is,
however, neither a defect nor a fault – as if truth were a pure
unconcealment that has rid itself of everything concealed. If truth
could accomplish this it would no longer be itself. Denial, by way of
the twofold concealing, belongs to the essence of truth as
unconcealment. Truth, in its essence, is un-truth. We put it this way
emphatically to indicate, with a perhaps off-putting directness, that
refusal in the mode of concealing is intrinsic to unconcealment as
clearing. On the other hand, the sentence "the essence of truth is
un-truth" should not be taken to claim that truth, fundamentally, is
falsehood. Equally little does it mean that truth is never itself but,
dialectically represented, is always its opposite as well. (The
Origin of the Work of Art (GA5) 1935/36,
So all very saṃsāra and Maya. The final recommendation is to let go of ascertainment, in a disavowal. Again from Being & Time (386):
Arising, as it does, from a resolute projection of oneself,
repetition does not let itself be persuaded of something by what is
'past', just in order that this, as something which was formerly
actual, may recur. Rather, the repetition makes a reciprocative
rejoinder to the possibility of that existence which has-been-there.
But when such a rejoinder is made to this possibility in a resolution,
it is made in a moment of vision; and as such it is at the same time
a disavowal of that which in the "today", is working itself out as
the 'past'.1 Repetition does not abandon itself to that which is past,
nor does it aim at progress. In the moment of vision authentic
existence is indifferent to both these alternatives.
(footnote 1. The idea seems to be that in resolute repetition one is
having, as it were, a conversation with the past, in which the past
proposes certain possibilities for adoption, but in which one makes a
rejoinder to this proposal by 'reciprocating' with the proposal of
other possibilities as a sort of rebuke to the past, which one now
Again, all very buddhist. "That brahmana who does not grasp at a view, with what could he be identified in the world?" Sn 4.5
So we should believe in the existence of other minds with a grain of disbelief?
Pragmatically you have to go with what you know and roll the dice. The problem comes with identification. I'll finish with this quirky quote from Alfred Korzybski, Science & Sanity, 4th ed, page 187.
Identification, or the confusion of orders of abstractions, in an
aristotelian or infantile system, plays a much more pernicious role than the present official psychiatry recognizes. Any
identification, at any level, or of any orders, represents a
non-survival s.r [semantic reaction] which leads invariably to the
reversal of the natural survival order, and becomes the foundation for
general improper evaluation, and, therefore, general lack of adjustment, no matter whether the maladjustment is subtle as in daily
life, or whether it is aggravated as in cases of schizophrenia. A
non-aristotelian system, by a complete elimination of 'identity' and identification, supplies simple yet effective means for the
elimination by preventive education of this general source of
So basically, don't worry about it. Don't get hung up on labels. Other minds, maybe. It's sure going to get confusing with AI.