Again, most of the chief distinctions marked by economic terms are differences not of kind but of degree.

I admit that these terms and the diagrams connected with them repel some readers, and fill others with the vain imagination that they have mastered difficult economics problems, when really they have done little more than learn the language in which parts of those problems can be expressed, and the machinery by which they can be handled. When the actual conditions of particular problems have not been studied, such knowledge is little better than a derrick for sinking oil-wells erected where there are no oil-bearing strata.

Knowledge is our most powerful engine of production.

But if inventions have increased man's power over nature very much, then the real value of money is better measured for some purposes in labour than in commodities.

Political Economy or Economics is a study of mankind in the ordinary business of life.

In common use almost every word has many shades of meaning, and therefore needs to be interpreted by the context.

Again, most of the chief distinctions marked by economic terms are differences not of kind but of degree.