The perceptual conscious system is directed onto the external world, it mediates perceptions of it, and in it is generated, while it is functioning, the phenomenon of consciousness. It is the sense organ of the whole apparatus, receptive, moreover, not only of excitations from without but also of such as proceed from the interior of the mind. One can hardly go wrong in regarding the ego as that part of the id which has been modified by its proximity to the external world and the influence that the latter has had on it, and which serves the purpose of receiving stimuli in protecting the organism from them, like the cortical layer with which a particle of living substance surrounds itself.
This relation to the external world is decisive for the ego. The ego has taken over the task of representing the external world for the id, and so of saving it; for the id, largely striving to gratify its instincts and complete disregard of the superior strength of outside forces, cannot otherwise escape annihilation.
In the fulfillment of this function, the ego has to observe the external world and preserve a true picture of it in the memory traces left by its perceptions, and, by means of the reality test, it has to eliminate any element in this picture of the external world which is a contribution from internal sources of excitation.
On behalf of the id, the ego controls the path of access to motility, but it interpolates between desire and action the procrastinating factor of thought, during which it makes use of the residue of experience stored up in memory. In this way it dethrones the pleasure principle, which exerts undisputed sway over the process and adds and substitutes for it the reality principle, which promises greater security and greater success.
The relation to time, to, which is so hard to describe, is communicated to the ego by the perceptual system; indeed it can hardly be doubted that the mode in which the system works is the source of the idea of time. What, however, especially marks the ego out and contradistinction to the id, is a tendency to synthesize its contents, to bring together and unify its mental processes which is entirely absent from the id.
When we come to deal presently with the instincts and mental life, I hope we shall succeed in tracing this fundamental characteristic of the ego to its source. It is this alone that produces the high degree of organization which the ego needs for its highest achievements. The ego advances from the function of perceiving instincts to that of controlling them, but the latter is only achieved through the mental representative of the instinct becoming subordinate to a larger organization, and finding its place in a coherent unity. In popular language, we may say that the ego stands for reason and circumspection, while the id stands for untamed passions.
You may, however, raise the question why these people, whether they write books or make conversation, should behave so badly, and you are inclined to the view that the cause does not lie entirely with the people themselves... [W]hat you meet with in literature and conversation in the shape of prejudice is the aftereffect of an earlier judgment, the judgment, namely, which the representatives of official science have passed upon the young science...
I have already complained about it once before in a historical survey of the subject, and I shall not do so again – perhaps even that was once too often; but indeed there was no logical blunder, no offense against decency and good taste which the scientific opponents did not permit themselves in those days. What was a situation such as actually occurred in the Middle Ages, in which a wrongdoer, or even a mere political opponent, was put in the pillory and exposed to the ill-treatment of the mob. And perhaps you do not fully realize how high up in our society the mob spirit extends, and to what lengths people will go on a field that they are a part of a crowd and superior to personal responsibility.
At the beginning of those times I stood more or less alone, and very soon polemics would do no good, and that complaints and appeals to worthier minds were senseless, since there were no courts before which one could plead one's cause. That being so, I took another path; I made use of applied psycho-analysis for the first time by explaining the behavior of the crowd as an expression of the same resistance which I had to struggle against in my individual patients.
Kept off all polemics and influence my followers gradually gathered to do the same. This mode of behavior was satisfactory. The ban under which analysis was placed in those days has since been lifted; but, just as a belief which has been given up lingers on as a superstition, just as a theory which science has abandon is preserved as a popular belief, so to today does the original excommunication from scientific circles survives in the mocking contempt of the writers and conversationalists. You will therefore no longer be surprised at their behavior.
You must not, however, expect the good news that the struggle is at an end... [T]here is no question of that; the battle still going on, but in a more respectable way. There is another new factor, and that is that in the scientific world a kind of buffer state has been formed between analysis and its opponents, consisting of people who allow that there is something in analysis (and even believe in it, subject to the most diverting reservations), but who, on the other hand, reject other parts of it as they are eager to let everyone. What determines their choice is not easy to guess . It seems to be a matter of personal sympathies .
-Excerpts from New Introductory Lectures on Psycho-Analysis by Sigmund Freud 1933
pages 105-107, 188-189