I can agree with Clive James' general definition of humanism while disagreeing with the fogeyish particulars of his argument in Cultural Amnesia:
Humanism was a particularized but unconfined concern with all the high-quality products of the creative impulse, which could be distinguished from the destructive one by its propensity to increase the variety of the created world rather than reduce it.
Note how this chimes with Lionel Trilling's definition of liberalism in The Liberal Imagination (in a fragment from a 1974 lecture printed as a foreword to the 1976 edition): "...liberalism was...a political position which affirmed the value of individual existence in all its variousness, complexity, and difficulty." He goes on to identify literature, "especially the novel," as "the human activity which takes the fullest and most precise account of variousness, complexity, difficulty--and possibility."
We can thus understand the novel as the artistic expression of liberalism, and liberalism itself as the political expression of humanism. But all three constructs also point toward an even more fundamental idea that grounds them all: pluralism. Pluralism is the fertile soil in which these ideas grow, the garden where humanism bequeaths liberalism which begets Middlemarch and Ulysses, Gravity's Rainbow and Howard's End.
It is tragically telling that both these definitions are matters of "was," past tense epitaphs for ideas gone. In a fascisizing, Trumped-out America that neither writer could have predicted (imagine how it would've horrified Trilling), the past tense seems especially disheartening. For pluralism, humanism, liberalism are exactly the medicines America needs today. We need them in gigantic surreal syringes out of William Burroughs' wettest dreams. We need megadoses to flush this fascist psychosis out of our country and make America recognizable again. For in America in the middle of 2018, the yes-or-no question many African-Americans are asking themselves--"Have white people lost their damn minds?"--solicits one obvious answer--and it's not the comforting one.