Extending a common proverb, Wollstonecraft argues that just as invention is born of necessity, so is virtue. The person raised in ease and flattery — sheltered from difficulty, never required to exercise independent judgment — does not acquire virtue; they acquire the appearance of inoffensiveness, which is a very different thing. Real moral strength requires something to strengthen against.
The image Wollstonecraft uses is striking: a person raised in a "torrid zone" of pleasure and flattery — where the sun of gratification beats down without respite — is incapable of the self-command that moral life requires. This is precisely the condition of women educated only for attractiveness. Without adversity, without the exercise of understanding, without the friction of the world, the character cannot develop the resilience that virtue demands.
Wollstonecraft ties virtue directly to the hierarchy of human worth. Virtue is the acquirement that places one human being above another — not birth, not beauty, not rank. And virtue, being an acquirement, requires reason, education, and the freedom to develop and exercise one's faculties. On this view, the exclusion of women from serious education is not merely an injustice — it is the systematic prevention of their moral development, a wrong done to them as human beings.
The virtue argument appears most directly in Chapter IV of the Vindication. Wollstonecraft's ethical framework draws on rationalist moral philosophy and anticipates themes in Kantian duty ethics, though her primary concern is political rather than purely philosophical.