The Inductive Methods described in the preceding chapter can only be applied fruitfully where the facts investigated can be analysed adequately, and examined under sufficiently varied conditions. This is equally true of the more advanced methods which will be considered later. Now these requirements cannot always be satisfied. The facts investigated may be too complicated for adequate analysis, and may not be observable under sufficiently varied circumstances. In such cases it is impossible to ascertain with confidence the thread of connection between conditions and consequents by means of the above-mentioned inductive methods. The kind of facts here considered may be indicated by reference to meteorological, economic, social, medical and various biological problems.