Galen is exercised to assert the reliability of one’s fundamental intuitions and sense-perceptions (what is trustworthy in itself, ex heautou pista), on the one hand, while giving an explanation of human disagreement on matters of fact and theory, on the other. His view is that while we are endowed with a naturally reliable evaluative faculty (kritērion), there is a right and a wrong way of training this; the former will, in particular, enable one to distinguish true from false arguments. (Training of the individual faculties of sense perception—for example, touch—is also of great importance, especially for the aspiring doctor.) Galen uses an analogy with other specialist skills (technai): a music teacher or gymnastic trainer, equally, relies on the pupil’s trust in his own natural kritērion, but this does not mean that performance will be error-free. Rather, teaching in these contexts—as in that of logical argument and knowledge acquisition—is a constant process of supervision and correction of errors.