The argument as far as 205 is simply and clearly laid out by Munro, but later editors have rejected his explanation, and proposed more involved analyses. The first purpose of this paper is to support the simple interpretation and refute later complications.

The only serious difficulty lies in the mention of plants in line 189. Without this line the argument would run as follows. ‘Nothing can move upwards of its own accord’ (184–6). ‘Don&t be misled by the atoms of flames, for they spring into being and take their increase in an upward direction, although all weights, left to themselves, move downwards’ (187–90). ‘Nor must we believe that when fire leaps up to the roofs of houses …, it does so of its own accord’ (191–3). Now the two analogicalarguments: ‘For blood spurts up into the air and timbers leap out of the water, yet everybody agrees that their weights left to themselves move downwards’ (194–202). Now the conclusion repeating the original proposition: ‘This is how it must be that flames too rise, forced out upwards through the air although their weights, left to themselves, move downwards’ (203–5).