Investment may be counted on the gross or the net basis. Net investment is gross investment minus depreciation. Investment may be ex-ante or planned or anticipated or intended investment; or it may be ex-post, i.e., actually realised investment, or when investment is not merely planned or intended, but which has actually been invested or implemented. This is so true when buying investment properties.
Another classification of investment may be private investment or public investment. Private investment is on private account, i.e., by private individuals, and public investment is by the government. Private investment is influenced by marginal efficiency of capital i.e., profit expectations and the rate of interest. It is profit-elastic. Public investment is by the regional or local authorities, such as building of roads, public parks etc. In public investment, profit motive does not enter into consideration. It is undertaken for social good and not for private gain.
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.