Later in life the pair of friends who were once comrades go into different professions that fill the mind with special professional ideas and induce different habits of thought. Each will be conscious, when they meet, that there is a great range of ideas in the other's mind from which he is excluded, and each will have a difficulty in keeping within the smaller range of ideas that they have now in common; so that they will no longer be able to let their _whole_ minds play together as they used to do, and they will probably feel more at ease with mere acquaintances who have what is _now_ their knowledge, what are now their mental habits, than with the friend of their boyhood who is without them. This is strongly felt by men who go through a large experience at a distance from their early home and then return for a while to the old place and old associates, and find that it is only a part of themselves that is acceptable. New growths of self have taken place in distant regions, by travel, by study, by intercourse with mankind; and these new growths, though they may be more valuable than any others, are of no practical use, of no social availableness, in the little circle that has remained in the old ways. Then there are changes of temper that result from the fixing of the character by time. We think we remain the same, but that is one of our many illusions. We change, and we do not always change in the same way. One man becomes mellowed by advancing years, but another is hardened by them; one man's temper gains in sweetness and serenity as his intellect gains in light, another becomes dogmatic, peremptory, and bitter. Even when the change is the same for both, it may be unfavorable to their intercourse. Two merry young hearts may enjoy each other's company, when they would find each other dull and flat if the sparkle of the early effervescence were all spent. I have not yet touched upon change of opinion as a cause of the death of friendship, but it is one of the most common causes. It would be a calumny on the intelligence of the better part of mankind to say that they always desire to hear repeated exactly what they say themselves, though that is really the desire of the unintelligent; but the cleverest people like to hear new and additional reasons in support of the opinions they hold already; and they do not like to hear reasons, hitherto unsuspected, that go to the support of opinions different from their own. Therefore a slow divergence of opinion may carry two friends farther and farther apart by narrowing the subjects of their intercourse, or a sudden intellectual revolution in one of them may effect an immediate and irreparable breach.