Abstract
In the article theoretical deliberations relating to impact of propensities on basic macroeconomic phenomena were presented. A general definition of propensity was discussed. The influence of propensity for consumption, propensity for investment and propensity for thesaurization on national income, interest rates, consumption expenditures, investments and money supply was analyzed. Derivatives that make it possible to identify quantitative effects of propensities were introduced. On the basis of the discussed Keynesian model it is possible to say that the propensity to consume increases interest rate and national income, the propensity to invest makes investments, national income and interest rates higher and the propensity for thesaurization could increase interest rates by lowering money supply.