Investment which is independent of the level of income, is called autonomous investment. Such investment does not vary with the level of income. In other words, it is income-inelastic. Autonomous investment depends more on population growth and technical progress than on anything else. The influence of change in income is not altogether ruled out, because higher income would probably result in more investment. But the influence of income is negligible as compared with the influence of population growth and progress of technical knowledge.
Examples of autonomous investment are long-range investments in houses, roads, public buildings and other forms of public investment. Most of the investment is undertaken to promote planned economic development. It also includes long-range investment to bring about technical progress or innovations. Public investment means investment which occurs in direct response to invention, and much of the long-range investment, which is only expected to pay for itself over a long period, can be regarded as autonomous investments.