But if the lives and the writings of the alchemists so clearly establish the physical nature of the Hermetic aim and _opus_, it may well be demanded how a psychical or moral interpretation could be reasonably set upon the symbols and the ambition of all the adepts. Such interpretations can never be wholly exonerated from the charge of extravagance, and of a purblind indifference to the most plain and notorious facts, but they may be to some extent justified by a consideration of the allegorical methods of the alchemists and by the nature of the Hermetic theory. The profound subtleties of thought seldom find adequate expression even when the whole strength of a truly intellectual nature is brought to bear upon the resources of language, and where the force of direct appeal is unwillingly acknowledged to be insufficient, the vague generalities of allegory can scarcely be expected to succeed. It is the province of symbolism to suggest thought, and the interpretation of any sequence of typology inevitably varies in direct proportion with the various types of mind. Each individual symbol embodies a definite conception existing in the mind of its inventor, and in that symbol more or less perfectly expressed, but every student of allegory out of every individual symbol extracts his own meaning, so that the significance of typology is as infinite as the varieties of interpreting intelligence. For this reason, the best and truest adepts have always insisted on the necessity of an initiated teacher, or of a special intellectual illumination which they term the grace of God, for the discovery of the actual secret of the Hermetic art. Without this light or guidance the unelected student is likely to be adrift for ever on a chaotic sea of symbols, and the _prima materia_, concealed by innumerable names and contradictory or illusory descriptions, will for ever escape him. It is in this way that a thousand unassisted investigators have operated upon ten thousand material substances, and have never remotely approached the manufacture of the Grand Magisterium, and, after the same manner, outwearied by perpetual failures in the physical process, that others have rejected the common opinion concerning the object of alchemy, and with imaginations at work upon the loftier aspirations expressed by Hermetic adepts, have accredited them with an exclusively spiritual aim, and with the possession of exclusively spiritual secrets.