Was sin possible in the Garden of Eden?

Henri Blocher, in his book that only he, Don Carson and God fully understand, writes:
This is why I would even question the usual way of speaking of sin's possibility in Eden. On the surface, nothing could be more obvious; since it happened, it must previously have been possible. But is the application of this logic justified? Actually, it presupposes a continuity, a homogenous field of virtualities and actualities... whereas applying the logic to the first intrusion of sin involves a subtle, hidden denial of the discontinuity of sin, that is, of its radical strangeness. Certainly sin was not impossible; the human being was not immutable. In that sense, one could speak of a merely theoretical possibility of sin. But a [not] real possibility, to borrow Kierkegaard's significant phrase.