The other two categories are of more significance. They help, for example, to explain how certain things may be called “causes” even though they do not always bring about the effect in question. Antecedent causes are conditions which raise the likelihood of an outcome in a body (say, the occurrence of a disease); these are typically external conditions, for example extreme ambient heat or moisture. But the presence of such causes does not guarantee the outcome; this will depend on internal differences in the constitution of the bodies in question, and in particular a preceding cause will be required as trigger. Galen explores the problem through the example of a person who contracts fever as a consequence of exposure to heat in a public stadium. Not everyone present in the stadium at the same time was similarly affected; but this does not mean that exposure to heat was not correctly identified as a (part) cause. It is, namely, an antecedent cause, which will only produce the pathological outcome in conjuction with the relevant preceding (internal) cause. Again, Galen uses this framework in an epistemologically optimistic way, highlighting the ability of the expert to predict or correctly analyse such an outcome, given sufficient understanding of all the relevant causal features.