The turmoil of the 1960's, and the sf New Wave invasion, hit Silverberg hard; from being a facile, million-words-a-year writer, he fell prey to the fears and insecurities of ordinary mortals, and his output dwindled accordingly. His rehabilitation, into a consummate craftsman of limited but perfectly worked-out ideas, proceeded through the 1968-74 period covered by the 27 tales collected here. Not surprisingly, then, the ideas are eclectic but the themes dwell on searches for meaning and quests for reality and stability in the face of agonizing doubts (per the title); the characters ask many questions but discover few answers, and many of the stories are weakly or implausibly concluded. In the usual Silverberg mode, there are some notable time-travel variations. A man wanders freely in time and probability, but is inevitably drawn back to the woman he loves; though the original is irrecoverable, he discovers new probabilistic versions of her. A feuding couple each fantasize about killing the other via time travel (wittily, Silverberg even deals with the old paradox about going back in time to kill one's grandfather). Three versions of one man--one in the present, one two days in the future, one two days in the past--confer telepathically to play the stock market. A future newspaper shows up, conferring temporary bene. fits on the recipients--but the future collapses into a terrifying blank. And there are other tales exploring circular time, telepathy, aliens, mutants, and telekinesis--not to mention yarns about: Jewish aliens, lovelorn dolphins, a robot pope, religious ecstasy, compulsory organ donations, disaster as entertainment, split brains, intelligent stars, and much more. A provocative spectrum, then, and a fascinating window on to the process of a fine writer feeling his way towards maturity.