Economics isn't science, and while Ricardo has some brilliant insights, it isn't a science; he barely models anything. It isn't even a hypothesis since you can never really test it. The core of his idea is this:

the rate of profits can never be increased but by a fall in wages [...] If, therefore, by the extension of foreign trade, or by improvements in machinery, the food and necessaries of the labourer can be brought to market at a reduced price, profits will rise.

I.e., use trade to get to lower wages