There can be no doubt that savages are capable of general and abstract ideas; and no one now supposes that language is an adequate measure of thought. A language contains names only for things, groups, and aspects or actions of things which the people who use it need to discuss: if they do not need to speak of abstractions, there are no words for them. But we cannot assume of the contents of the mind, any more than of the outside world, that things do not exist unless we have noticed and named them. Professor Franz Boas has shown[96] that languages of the northern Amerinds, that do not idiomatically express abstract ideas, may be made to do so without violence, and that the abstract expression is intelligible to men native to the languages. “Every one who knows people of low culture,” says Dr. Rivers, “must recognise the difficulty which besets the study of any abstract question, not so much because the savage does not possess abstract ideas as that he has no words of his own to express them.”[97] Amongst the ideas attained by savages, and having an important part in their lives, though often taken for granted and unexpressed, are some of the highest generality: for example “force.” The notion of force is derived from the experience of effort in our own muscular exertions; but with the development of our perception of physical objects by the integration of sense-data—sight, touch, movement and resisted movement (kinæsthesis), smell, hearing—this sense of effort, being transferred to objects as equivalent to our own exertions about them, becomes the all-important core of every object (or meaning of every perception of an object), without which the thing would be a mere show, neither useful nor injurious—sheep and tigers, rocks and pumpkins alike indifferent. Probably the perceptions of all the higher animals (down to reptiles) have this meaning. Force is reality, and by primitive man is thought of as the essence of whatever he conceives of as real, such as spells, talismans and ghosts. Having a subjective ground, from which it never becomes free, the notion of it is indefinite, varies for each of us with our constitution, age, health, and not only lends itself to the wildest whims of superstition, but has misled scientific investigations.