The traditional concerns of moral reflection about war have been with the causes for which wars are begun and the methods by which they are conducted. Neither of these trains of thought can lead us directly to any conclusion about the instruments with which war is practised or prepared for. To speak of proportion and discrimination is to speak of ways of acting; but instruments are apparently adaptable to different ways of acting. The surgeon's scalpel can be used to commit murder, the pirate's cutlass to perform a surgical operation. It may seem, then, as though the contemporary concern over types of weapons can have no purchase in the traditional moral categories of intention and action. If instruments are neutral, what could possibly be said in general terms about the morality of different types of weapon, which might be used for moral or immoral purposes depending on those who used them?

But this doubt need not delay us long. If a scalpel can be used to commit a murder and a cutlass to perform an amputation, that does not mean there is no moral significance in the difference between the two implements. A surgeon's scalpel on the steward's requisition list for a merchant vessel would cause nobody any alarm; two dozen cutlasses might. The point is commonly made that instruments are designed in relation to purposes, and bear within their design the purposes they were conceived for. The form which weapons take tells us what kind of fighting is envisaged. The peculiar weapons of our age give voice to certain hypothetical war plans and are open to criticism inasmuch as the plans themselves are open to criticism.