But even if the serious aspect of the petroglyphs is granted there still remains the difficulty of determining their special purpose. The historical explanation, although it would appear the most natural for us to adopt, is not to be taken unreservedly with regard to tribes on a low degree of development. What to us seems a sort of picture-writing might possibly serve a purpose anything but communicative. The so-called ideograms of the Nicobarese have, for example, according to Herr Svoboda, for their object the distraction of the attention of the malevolent demons from their houses and implements[248]. When investigating the ritual, especially the funeral ceremonies, one meets with various specimens of similar ideography, the thought-conveying purpose of which is deceptive. By the above examples the ambiguous character of primitive art-works has been proved almost _ad nauseam_. It appears that every single conclusion based upon isolated ethnological examples only is liable to be upset after a closer study of the facts. In order, therefore, to make any positive assertions as to the commemorative element in art we need some safer and more reliable grounds of argument than the inconsistent stories of travellers. We have, in other words, to investigate the social and psychological conditions which, in the respective cases, speak for or against the assumption of a commemorative impulse as a motive for art-production. Owing to our deficient knowledge of primitive life we are not able to rely upon these social and psychological data in every individual case. But we may nevertheless arrive at some broad results which in the main tally with, and corroborate the evidence afforded by, the majority of ethnological facts.