Questions will arise at first only after our senses have discerned some recurring pattern or order in events. It is a recognition of some regularity, of some similar feature in otherwise different circumstances, which makes us wonder and ask "why?" Many such regularities of nature are recognized "intuitively" by our senses. We see and hear patterns as much as individual events without having to resort to intellectual operations. The distinction between a prediction of the appearance of a pattern of a certain class and a prediction of the appearance of a particular instance of this class is sometimes important also in the physical sciences. The distinction between simplicity and complexity raises considerable philosophical difficulties when applied to statements. The multiplicity of even the minimum of distinct elements required to produce a complex phenomenon of a particular kind creates problems which dominate the disciplines concerned with these phenomena, and makes such disciplines appear very different from those concerned with simpler phenomena.