WE have had something to say about those criteria which we cannot accept as in any way applicable to the dispute between vitalists and materialists. We must now come to that which is, in our opinion, the only true criterion.

We have already said that we believe living substance always to conform to the laws of physics and chemistry. We also believe that it is controlled by non-material influences which obey laws of their own. We hold, therefore, that living substance is subject to a double set of restrictions, that its behaviour is more determinate than that of lifeless substance. Our criterion is double determinateness. We assert that any evidence which proves the organic world to be subject to laws from which the inorganic -world is free is evidence for vitalism.

Is this criterion obvious or paradoxical? We should have thought it obvious did we not remind ourselves that the great Huxley coupled Matter and Causation, Spirit and Spontaneity, and that many others have done the same. So we fear that it will be necessary for us to elaborate our meaning a little. We think we can do so best with the help of an analogy. A game of chess will serve.

Let the chessmen moving from square to square during the course of the game correspond to small particles of substance moving from place to place in a living organism and let the rules of the game correspond to the laws of physics and chemistry. These rules demand that a Rook shall move only in straight horizontal or vertical lines, a Bishop diagonally and a King in any direction, but by only one square at a time. The rules prescribe to which squares a Knight may jump, that Pawns must march forward only but must take on the slant, they prescribe when castling may be performed and when a Pawn may be exchanged for a Queen. The rules of chess define the restrictions always imposed on the behaviour of the pieces in the same way as the laws of physics and chemistry define the restrictions imposed everywhere and at all times on the behaviour of particles of Matter.

Is the course of a game of chess determined by the rules? Partly. But only partly. It is also determined by the players. So a game of chess is doubly determinate. The players are influences separate from the chessmen. They are, therefore, analogous to the non-material influences which vitalism postulates.

Some card games are different; patience, for instance. The course of events is fully determined by the sequence of cards in the pack and the rules of the game. Here what happens is singly determinate. Materialists say that vital processes are analogous to these card games. Vitalists say that they are analogous to games of chess. We have to decide on the evidence available which is right.

Analogies are never perfect and the one we have chosen is no exception. But we may usefully pursue it a httle further. For this analogy may help to explain why we have rejected the three criteria which biologist-philosophers seem to adopt.

Consider first the late J. S. Haldane's criterion: dependence on environment. In the chess-analogy the environment of any piece is made up by all the other pieces on the board. The behaviour of each is dependent on this environment, for a good player takes careful note of the position of each chessman, even the humblest pawn, before deciding on a move. No one would say that the dependence of the moves on the configuration of all the pieces proved that the course of the game was due only to the unaided action of the pieces on each other. So why say that dependence on environment proves that no non-material influence such as Life can be there to act in accordance with the circumstances surrounding the individual?

Our analogy can serve equally well to illuminate the flaw in the second criterion: obedience to the laws of physics and chemistry. Does the fact that the course of a game of chess is controlled by influences separate from the chessmen imply that the rules are ever broken? No. They are not unless someone cheats. In exactly the same way vitalism does not imply in the least that the laws of physics and chemistry are ever broken, but only that, in addition, certain laws of biology are obeyed.

These laws are analogous to those principles of chess which good players do well to follow. Text-books on chess deal with some of the more obvious ones. They say that it is bad to have a "double Pawn". They explain that the best opening move is Pawn to King 4 and tell us what successive moves are advisable if the opening move is made by the Queen's Pawn instead. Whole books have been written on gambits and others could be devoted to the one subject of end play.

The less obvious principles of good play have not been formulated in text-books. They often defy translation into words. But they exist for all that. Each great chess-player has his own mode of procedure just as each animal has its own. mode of behaviour. It is true that biological laws are followed with greater consistency than the principles of good play in chess. They have become more stereotyped. But so we should expect if we consider how many times the same situations have arisen in the organic world and for how many millions of years.

Lastly, there is the criterion of causality. The fact that the course of a game of chess is controlled by influences separate from the chessmen does not preclude a predictable connection between cause and effect. If a player's Queen is threatened the effect is almost sure to be a move to protect her. If a Pawn is on the seventh square the next move is likely to be to the eighth square. In a first-class game it is often possible to predict several moves ahead. Games between champions are rarely played out because the ultimate result becomes evident to the players well before the final checkmate has been reached.

" But the course of a game of chess is not absolutely predictable," it may be objected. This is true. We can only predict with reasonable certainty when the situation is oft repeated and familiar. But in biology it is exactly the same. The laboratories in which Drosophila flies are bred are full of surprises.

Our evidence for vitalism will be, therefore, that in the organic world the course of events is more restricted than it is in the inorganic world, that more numerous and more stringent requirements have to be met; in. two words, that everything is doubly determinate. It will lead the reader to appreciate the nature of this evidence by easy stages if we begin with a little parable.

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