He wrote on this theme that,
It is easy to realise that the difference between the sexes concerns only the body - being, correctly, only this part that serves for the production of men. Since the mind participates only by giving its assent (and giving it in all people in the same manner), we can conclude that it is sexless.
In simple terms, de la Barre believed that men and women differed only in their reproductive organs. He thought that men and women were, by nature, the same in all other respects, including everything to do with the mind.
De la Barre drew some very modern, feminist conclusions from this idea. He asserted that traditional gender roles had no basis in "natural law" but were maintained by prejudice and custom alone.
(For instance, he complained that "legal scholars, who also have their prejudices, have attributed to nature a distinction that derives from custom alone.")
De la Barre claimed that,
the mind, not functioning differently in one sex than in the other, is equally capable of the same things
and therefore concluded that women were as equally suited as men (or more so) to be priests, generals and monarchs.
The argument framed by de la Barre eventually came to have much influence. But it can now be seen to be mistaken in its first assumption. Science is now demonstrating that the mind does have a sex. After a period of more than 300 years we can now conclusively reject the theory pioneered by de la Barre.
It has now finally become accepted in the scientific mainstream that there are significant differences between the male and female brain. A new book, The Female Brain, written by an American neuro-psychiatrist Louann Brizendine is the latest, and undoubtedly not the last, work to be published in this area (see the review by Janet Albrechtsen aptly titled "Feminism begs to differ, but unisex brain is a fantasy").
The scientific research should give heart to conservatives who have long held that there are naturally occurring differences between men and women which are hardwired into human biology.
(In fact, I think many conservatives would tend to the view that there is an essential masculinity to men and femininity to women, which forms a core part of our identity and which is reflected in traditional gender roles within the family and society.)