““If the abundance of wheat makes its value fall, the farmers will be less rich, because they have less exchange-values to obtain for themselves things that are necessary, useful or pleasant for life; but the consumers of wheat will profit from all that the farmers have lost: the loss of some will be compensated by the gain of others, and the general wealth will undergo no change” (pp. 108-09).” (p 208)
Marx's response is itself not as clear as it might be. He replies,
“Excuse me. The consumers of wheat eat the wheat and not the exchangeable value of the wheat. They are richer in means of subsistence, but not in exchangeable value. They have exchanged a small amount of their products—which have a high exchange-value because of their relative paucity as compared with the quantity of wheat for which they are exchanged—for the wheat. The farmers have now received the high exchange-value and the consumers a good deal of wheat of small exchange-value, so that now the latter are the poor ones and the farmers the rich.” (p 208)
What Marx means here is that increased supply of wheat does not change its total value. It simply reflects the fact that the same value is now contained in a much larger quantity of wheat. Each quarter now has less value, but the farmer has a correspondingly greater number of quarters to sell. The process of exchange does not involve the exchange of exchange value in respect of the final consumer.
The buyer of wheat does not buy it for its exchange-value, but for its use value. Similarly, the seller of wheat sells it because, for them, it has no use value. The buyer gives up exchange value, and obtains use value, whereas the seller gives up a use value, and obtains exchange value.
When the exchange value of wheat falls, the buyers of wheat can obtain more of it, for the same amount of exchange value. They do not, therefore, obtain more exchange value, but only more use value. But, having given up these use values, the farmers obtain exchange value, and this exchange value – money – would buy more wheat than it did previously, before the value of wheat fell.
It is not the case, as Ganilh suggests here, that there has been a transfer of wealth from farmers to buyers of wheat. If previously 1,000 tons of wheat exchanged for 100 metres of linen, because both represented 100 hours of general labour, then if 100 hours of labour produce 1500 tons of wheat, these will exchange for the 100 metres of linen. The exchange value of the former will have fallen and the latter risen, but, at the end of the exchange, both will be in possession of the same 100 hours of value. The only difference will be that the buyers of wheat will have this 100 hours of value in the form of 1500 rather than 1000 tons of wheat.