to mass-transmitted reports is more widespread among people, for a mass-transmitted report is conveyed by a large number of people, so it has many listeners who share in hearing it from that large number. By contrast, sensory perception is confined to those who have experienced it. If someone says, “I saw,” “I heard,” “I tasted,” “I touched,” or “I smelled,” how can he use this to establish a demonstration binding on someone else? Even supposing that a number of people shared those sensory perceptions with him, it does not follow that others perceived them. Those who have not perceived them can know of them only through reports.

Most of their universal knowledge concerning the properties of existing things consists of knowledge of the regular behavior of the thing concerned. This is what they call “propositions based on intuition.” Most of their rational knowledge of nature and their celestial sciences, such as astronomy, fall into the category of knowledge based on experience. No demonstration can be established in these matters, for most people know only through transmitted reports that these natural bodies and movements have been investigated experimentally. Mass transmission concerning such matters is rare. At most, an account of the relevant experience is transmitted from certain physicians or mathematicians.

The most one finds is Ptolemy saying, “This is something that so-and-so observed,” or Galen saying, “This is something I tested,” or, “So-and-so told me that he tested it.” None of this constitutes mass transmission. Even supposing that someone else also tested it, that is still a single report. Most people have not tested everything those men tested, nor have they learned through astronomical observations what those men claim to have