"The accepted idea that a common stock should sell at a certain ratio to its current earnings must be considered more the result of practical necessity than of logic. The market takes the trend or future prospects into account by varying this ratio for different types of companies. Common stocks of enterprises with only slight possibilities of increasing profits ordinarily sell at a rather low price-earning ratio (less than 15 times their current earnings); and the common stocks of companies with good prospects of increasing the earnings usually sell at high price-earnings ratio (over 15 times the current earnings)."
- Benjamin Graham