Descartes submitted his manuscript to many philosophers, theologians and a logician before publishing the Meditations. Their objections and his replies (many of which are quite extensive) were included in the first publication of the Meditations. In the Preface to the Meditations, Descartes asks the reader "not to pass judgment on the Meditations until they have been kind enough to read through all these objections and my replies to them.” Thus, this dialogue could be seen as an integral part of Descartes' views expressed in the Meditations.
The seven objectors were, in order (of the sets as they were published):
- The Dutch theologian Johannes Caterus (Johan de Kater) – first set of objections.
- Various "theologians and philosophers" gathered by Descartes' friend and principal correspondent, Friar Marin Mersenne – second set of objections
- The English philosopher Thomas Hobbes – third set of objections
- The theologian and logician Antoine Arnauld – fourth set
- The philosopher Pierre Gassendi – fifth set (Descartes wrote that all of these could be easily dismissed.)
- Another miscellany gathered by Mersenne – sixth set
- The Jesuit Pierre Bourdin – seventh set of objections
They make many objections to Descartes’ arguments and method. Some of the objections show that the objector has misunderstood the text, or wilfully misquoted it, as in the last set of objections by the Jesuit. Descartes’ response to these is often dismissive and curt. Other objections are more powerful, and in some cases it is controversial whether Descartes responds to them successfully (refer to Hobbes' objections). At times Descartes' demeanor suggests that he expected no criticisms would be forthcoming.
Some of the most powerful objections include the following:
Objections to proof(s) of God’s existence:
A. We have no (clear) idea of an infinite Being (1st, 2nd, and 5th objections).
B. From the fact that I can think of a perfect being, it doesn’t follow that the perfect being exists (1st, 2nd, and 5th).
C. We could get the idea of God without God’s causing the idea (2nd, 3rd).
D. Nothing can cause itself to exist (4th), so God can’t cause himself to exist unless God is composed of some essence that in and of itself has the property of timelessness.
Objections to the epistemology:
A. How can we be sure that what we think is a clear and distinct perception really is clear and distinct (3rd, 5th)?
B. Circle objection 1: if we aren’t certain that judgments based on clear and distinct ideas are true before we prove God’s existence, then we can’t be certain that we are a thinking thing (2nd). Circle objection 2: if we aren’t certain that clear and distinct ideas are true before we prove God’s existence, then we can’t be certain that God exists, since we use clear and distinct ideas to prove God’s existence (4th).
C. Contrary to what Descartes argues, we are certain that bodies exist/that perception coincides with reality (5th, 6th), but we are not certain that the bodies of our perception are actual bodies in an existent external world.
Objections to philosophy of mind:
A. Ideas are always imagistic (3rd), so we have no idea of thinking substance (non-image idea).
B. We can’t conclude that the mind (thinking thing) is not also a corporeal thing, unless we know that we know everything about the mind. But we don’t know that we know everything about the mind. So we don’t know that the mind isn’t corporeal. (2nd, 4th, 5th, 7th).
Elisabeth of Bohemia also corresponded with Descartes on the Meditations. She objected both to his description of the union between mind and body, and that virtue and moral truths seem to need to be grasped by something other than the intellect (despite Descartes's assertion that all truths must be grasped intellectually).