 Lewis (1946, 29–31) thought that necessary truths are knowable a priori, independently of experience. In applying concepts like those of red or apple to current experience, and so interpreting experience, we form expectations and make predictions about future experience, conditional on actions we might perform. Our beliefs constitute empirical knowledge in so far as past experience gives us good reason (largely inductive) for making these predictions. However, we aren’t making predictions about future experience simply in stating what these concepts are, and what their definitions are, and what defining criteria they provide for applying them to experience. Such statements are explicative, not predictive, and so neither falsifiable by failed prediction nor verifiable by successful prediction nor justified by inductive evidence. The a priori is what we are not required to abandon, no matter what experience may bring, and in that sense, true no matter what, and in that sense necessary (Lewis 1929, 267.) However, a priori principles are neither principles that are universal nor ones that we have to accept. The acceptance of a set of concepts is a matter of decision or legislation or the adoption of an intention to employ certain criteria in the interpretation of experience, something for which there are alternatives but for which the criteria are not empirical but pragmatic. 