この地で行った最初の省察について語るべきかどうか，わたしにはわからない。というのも，それはきわめて形而上学的で，普通一般から離れているので，すべての人の好みには合わないかもしれないからだ。だが，わたしが選んだ基礎が十分堅固であるかどうか判断してもらうため，それについて語ることは，ある意味でわたしの義務であると気づいた。生き方については，ひどく不確かだとわかっている意見でも，疑う余地のない場合とまった〈同じように，時にはそれに従う必要があると，わたしはずっと以前から認めていた。これは先にも述べたとおりである。だが当時わたしは，ただ真理の探究にのみ携わりたいと望んでいたので，これと正反対のことをしなければならないと考えた。ほんの少しでも疑いをかけうるものは全部，絶対的に誤りとして廃棄すべきであり，その後で，わたしの信念のなかにまったく疑いえない何かが残るかどうかを見きわめねばならない，と考えた。こうして，感覚は時にわたしたちを欺くから，感覚が想像させるとおりのものは何も存在しないと想定しようとした。次に，幾何学の最も単純なことがらについてさえ，推論をまちがえて誤謬推理をおかす人がいるのだから，わたしもまた他のだれとも同じく誤りうると判断して，以前には論証とみなしていた推理をすべて偽として捨て去った。最後に，わたしたちが目覚めているときに持つ思考がすべてそのまま眠っているときにも現れうる，しかもその場合真であるものは一つもないことを考えて，わたしは，それまで自分の精神のなかに入っていたすべては，夢の幻想と同じょぅに真でないと仮定しょぅ，と決めた。しかしそのすぐ後で，次のことに気がついた。すなわち，このようにすべてを偽と考えようとする間も，そう考えているこのわたしは必然的に何ものかでなければならない，と。そして「わたしは考える，ゆえにわたしは存在する〔ワレ唯ウ，故ニワレ在リ〕」というこの真理は，懐疑論者たちのどんな途方もない想定といえども揺るがしえないほど堅固で確実なのを認め，この真理を，求めていた哲学の第一原理として，ためらうことなく受け入れられる，と判断した。
I AM in doubt as to the propriety of making
my first meditations in the place above mentioned
matter of discourse; for these are so metaphysical,
and so uncommon, as not, perhaps, to be acceptable
to every one. And yet, that it may be determined
whether the foundations that I have laid
are sufficiently secure, I find myself in
a measure constrained to advert to them.
I had long before remarked that, in (relation
to) practice, it is sometimes necessary to
adopt, as if above doubt, opinions which
we discern to be highly uncertain, as has
been already said; but as I then desired
to give my attention solely to the search
after truth, I thought that a procedure exactly
the opposite was called for, and that I ought
to reject as absolutely false all opinions
in regard to which I could suppose the least
ground for doubt, in order to ascertain whether
after that there remained aught in my belief
that was wholly indubitable. Accordingly,
seeing that our senses sometimes deceive
us, I was willing to suppose that there existed
nothing really such as they presented to
us; and because some men err in reasoning,
and fall into paralogisms, even on the simplest
matters of Geometry, I, convinced that I
was as open to error as any other, rejected
as false all the reasonings I had hitherto
taken for demonstrations; and finally, when
I considered that the very same thoughts
(presentations) which we experience when
awake may also be experienced when we are
asleep, while there is at that time not one
of them true, I supposed that all the objects
(presentations) that had ever entered into
my mind when awake, had in them no more truth
than the illusions of my dreams. But immediately
upon this I observed that, whilst I thus
wished to think that all was false, it was
absolutely necessary that I, who thus thought,
should be somewhat; and as I observed that
this truth, I think, hence I am, was so certain
and of such evidence, that no ground of doubt,
however extravagant, could be alleged by
the Sceptics capable of shaking it, I concluded
that I might, without scruple, accept it
as the first principle of the Philosophy
of which I was in search.