Thinking about a necessary being › What necessity adds in chapter III

Chapter III strengthens the result Anselm claims. It argues that a being whose nonexistence cannot be conceived is greater than one whose nonexistence can be conceived. A supposedly unsurpassable being that could be thought not to exist would consequently be surpassed. Anselm concludes that God cannot be conceived not to exist.

Necessary existence, in this discussion, contrasts with an existence that can fail. It does not mean being very old, lasting a long time, or resisting destruction exceptionally well. A thing could last throughout an indefinitely long period while its existence still depended on conditions that might not have obtained.

Chapter II and chapter III therefore have distinguishable targets. The former argues against existence only in the understanding. The latter argues against conceivable nonexistence. Reading the second as merely repeating the first loses the further claim Anselm wants to make.

The further claim does not remove every difficulty. A reader can ask whether inconceivability here tracks reality or a limitation in the person doing the conceiving. Failure to imagine an object's absence is different from establishing that its absence is impossible. Anselm's argument invokes what belongs to understanding the unsurpassable being, rather than a report that he personally finds imagining its absence difficult.

This is also a reason to avoid turning the passage into a modern possible-worlds proof without explanation. The text proceeds through greatness and conceivability. A later formal reconstruction would need to state its own interpretation of possibility and the rules connecting possibility with necessity. Those additions should be assessed as additions, not silently attributed to Anselm.