"When we apprehend that it is impossible a thing can arise from nothing, this proposition ex nihilo nihil fit, is not considered as something existing, or as the mode of a thing, but as an eternal truth having its seat in our mind, and is called a common notion or . Of this class are the following: It is impossible the same thing can at once be and not be; what is done cannot be undone; he who thinks must exist while he thinks; and innumerable others, the whole of which it is... difficult to enumerate, but... if blinded by no prejudices, we cannot fail to know them when... thinking them..."