(a) Negative (preventive) checks

These are voluntary measures which control population by reducing the growth rate i.e. they are measures that slow birth rate. For this Malthus advocated for moral restraints, late marriage, celibacy etc.

(b) Positive checks

These are involuntary measures which control population by increasing the death rates.

This measure according to Malthus, inevitably comes in to control the population if people fail to control the population growth themselves. These measures come or appear in the form of famine starvation, wars, conflicts, diseases, calamities etc.