[P]opulation, when unchecked, goes on doubling itself every twenty-five years, or increases in a geometrical ratio. ... [T]he means of subsistence, under circumstances the most favorable to human industry, could not possibly be made to increase faster than in an arithmetical ratio.

With regard to the duration of human life, there does not appear to have existed from the earliest ages of the world to the present moment the smallest permanent symptom or indication of increasing prolongation.

Where there are few people, and a great quantity of fertile land, the power of the earth to afford a yearly increase of food may be compared to a great reservoir of water, supplied by a moderate stream. The faster population increases, the more help will be got to draw off the water, and consequently an increasing quantity will be taken every year. But the sooner, undoubtedly, will the reservoir be exhausted, and the streams only remain.

It is an acknowledged truth in philosophy that a just theory will always be confirmed by experiment.

The great and unlooked for discoveries that have taken place of late years have all concurred to lead many men into the opinion that we were touching on a period big with the most important changes.

I do not know that any writer has supposed that on this earth man will ultimately be able to live without food.

Evil exists in the world not to create despair but activity.