Today's readers must realize that Conquest is a product of its times. Russell was considered to be a liberal and open-minded man of his day, but he could not have anticipated the sensibilities of these days. Many statements in Conquest would be considered sexist or racist today. Stereotyped gender roles are assumed without apology, and "man" is often used as a synonym for "human".
Hypothetical examples are almost always of males, unless some stereotypic quality of women is being referred to. (If you can overlook the patriarchal form of Russell's language, what he says is often surprisingly feminist. "The relation of the mother to the child will have in the future to resemble more and more that which at present the father has, if women's lives are to be freed from unnecessary slavery.")
Statements about blacks or other non European races, though not hostile, clearly assume that the reader does not belong to these races. Statements that mention Jews tend to be complimentary, but are stereotypes nonetheless. It is better to propose that we simply emend the text in our minds, adding inclusive language as necessary, rather than berate Russell for the shortcomings of his era.
Almost any statement that Russell makes about animals is a projection. Consider, for example, the first line of the book: "Animals are happy so long as they have health and enough to eat." Did he acquire this knowledge through conversation or by telepathy? Animals frequently play for Russell the role that "the noble savage" played for Rousseau; they represent nature unaffected by civilization.
The Conquest of Happiness contains a number of historical misperceptions that were common among liberal intellectuals of the day. For example, the
Soviet Union was thought to be a grand experiment, with no hint of the police state horrors that we are now so well aware of. "The creation of an organization may be of supreme importance. So is the work of those few statesmen who have devoted their lives to producing order out of chaos, of whom Lenin is the supreme type in our day." Again, it is suggested that we should simply shake our heads and move on.
Psychological terminology has changed greatly in the last eight decades. Nervous fatigue, for example, refers to a variety of conditions that we now might call depression or stress or chronic anxiety. Fortunately, Russell uses a number of hypothetical examples, so it is usually not difficult to guess what his psychological terminology must mean.
Russell wrote this book long before the advent of anti-depressant drugs, and so he cannot be expected to know or discuss the physiological aspects of happiness and unhappiness. (Though he does speculate "Perhaps when biochemistry has made further advances we shall all be able to take tablets that will ensure our having an interest in everything.") The extent to which attitude, mood, or temperament is the result of brain chemistry or genetic makeup is something that a man of 1930 could not have understood as well as we do today.
Further caveats are given by Russell in the first chapter: "I shall confine my attention to those who are not subject to any extreme cause of outward misery." In other words, if you object that Russell's prescriptions are not adequate to find happiness for people in abject poverty, in great physical pain, or subject to persecution of one sort or another, Russell would probably have agreed with you. He also acknowledges that the causes of much unhappiness:
"lie partly in the social system, partly in individual psychology -- which, of course, is itself to a considerable extent a product of the social system. I have written before about the changes in the social system required to promote happiness. Concerning the abolition of war, of economic exploitation, or education in cruelty and fear, it is not my intention to speak in this volume."