Book, Paragraph

 1  II, 7 |    if he refers his problems back to all of them, he will
 2 VIII, 5|   the movent that is further back in the series as well as
 3 VIII, 5|     however, could be traced back, as we said before, until
 4 VIII, 8|      for the thing must turn back, and that which turns back
 5 VIII, 8|   back, and that which turns back in a straight line undergoes
 6 VIII, 8|      and there is no turning back they arrest each other,
 7 VIII, 8|     is the fact that turning back necessarily implies coming
 8 VIII, 8|      without a break or turn back again when it has reached
 9 VIII, 8|   case of a thing that turns back in its course we must do
10 VIII, 8| proceeds to D and then turns back and proceeds downwards again:
11 VIII, 8|   Therefore that which turns back in traversing a rectilinear
12 VIII, 8|      so until it has arrived back at A. Then when it is undergoing
13 VIII, 9| straight line is if it turns back a composite motion, in fact
14 VIII, 9|    while if it does not turn back it is incomplete and perishable: