 Most empiricists present complementary lines of thought. First, they develop accounts of how experience alone -- sense experience, reflective experience, or a combination of the two -- provides the information that rationalists cite, insofar as we have it in the first place. Second, while empiricists attack the rationalists’ accounts of how reason is a primary source of concepts or knowledge, they show that reflective understanding can and usually does supply some of the missing links (famously, Locke believed that our idea of substance, in general, is a composite idea, incorporating elements derived from both sensation and reflection, e.g. Essay, 2.23.2).