Prejudice is an Enemy of Reason

We shall expose the origin and trace the history of general errors, which have more or less contributed to retard or suspend the advance of reason, and sometimes even, as much as political events, have been the cause of man’s taking a retrograde course towards ignorance.

Those operations of the mind that lead to or retain us in error, from the subtle paralogism, by which the most penetrating mind may be deceived, to the mad reveries of enthusiasts, belong equally, with that just mode of reasoning that conducts us to truth, to the theory of the development of our individual faculties; and for the same reason, the manner in which general errors are introduced, propagated, trasmitted, and rendered permanent among nations, forms a part of the picture of the progress of the human mind. Like truths which improve and enlighten it, they are the consequence of its activity, and of the disproportion that always exists between what it actually knows, what it has the desire to know, and what it conceives there is a necessity of acquiring.

It is even apparent, that, from the general laws of the development of our faculties, certain prejudices must necessarily spring up in each stage of our progress, and extend their seductive influence beyond that stage; because men retain the errors of their infancy, their country, and the age in which they live, long after the truths necessary to the removal of those errors are acknowledged.

In short, there exist, at all times and in all countries, different prejudices, according to the degree of illumination of the different classes of men, and according to their professions. If the prejudices of philosophers be impediments to new acquisitions of truth, those of the less enlighted classes retard the propagation of truths already known, and those of esteemed and powerful professions oppose like obstacles. These are the three kinds of enemies which reason is continually obliged to encounter, and over which she frequently does not triumph till after a long and painful struggle. The history of these contests, together with that of the rise, triumph, and fall of prejudice, will occupy a considerable place in this work, and will by no means form the least important or least useful part of it.

It is a cognitive bias, and it prevents the acquisition of new truths.