Time Is the Simplest Thing by Clifford D. Simak

a sort of conditioned reflex action to escape the danger.
    It was something that he had no way of knowing how to do, that a short minute earlier he would have sworn would be impossible that he do. It was something that no human had ever done before, that no human would have ever dreamed of trying.
    For he had moved through time. He had gone into the past a half an hour or so.
    He stood in the street, attempting to recall how he might have done it, but all he could remember was the mounting terror that had come rolling, wave on wave, to drown him. There was one answer only: He had done it as a matter of deep-seated knowledge which he had not been aware of having and had accomplished it only as a final, desperate, instinctive effort—as one might, without thinking, throw up an arm to ward off an unexpected blow.
    As a human it would have been beyond his capability, but it would not, undoubtedly, have been impossible for the alien mind. As a human being he did not have the instinct, did not have even the beginning of the necessary know-how. It was an ability even outside the pale of paranormal action. There was no question of it: the only way he could have snapped himself through time was by the agency and through the courtesy of the alien mind.
    But the alien mind, it seemed, had left him; it was no longer with him. He hunted it and called it, and there was no trace and there was no answer.
    He turned to face the north and began to walk, keeping to the center of the street, marching through this ghost town of the past.
    The graveyard of the past, he thought. No life anywhere. Just the dead, bare stone and brick, the lifeless clay and wood.
    And where had gone the life?
    Why must the past be dead?
    And what had happened to that mind the alien on the distant star had exchanged with him?
    He sought for it again and he could not find it, but he did find traces of it; he found the spoor of it, tiny, muddy footprints that went across his brain; he found bits and pieces that it had left behind—strange, chaotic memories and straws of exotic, disconnected information that floated like flecks of jetsam in a frothy tide.
    He did not find it, but he found the answer to its going—the instinctive answer that suddenly was there. The mind had not gone and left him. It had, rather, finally, become a part of him. In the forge of fright and terror, in the chemistry of danger, there had been a psychologic factor that had welded the two of them together.
    And yet he still was human. Therefore, he told himself, the answer must be false. But it kept on persisting. There was no reason to it and there was no logic—for if he had two minds, if he were half human and half alien, there would be a difference. A difference he would notice.
    The business part of the street had dwindled to shabby residences, and up ahead of him he could see where the village ended—this village which half an hour ago (or a half an hour ahead?) had been most intent upon the killing of him.
    He halted for a moment and looked back and he could see the courthouse cupola and remembered that he’d left everything he owned back there, locked in the sheriff’s desk. He hesitated a moment, wondering if he should go back. It was a terrible thing to be without a dollar to his name, with all his pockets empty.
    If he went back, he thought, he could steal a car. If there were none with the keys left in the lock, he could short-circuit the ignition. He should have thought of it before, he told himself. The cars were standing there, waiting to be taken.
    He turned and started back. He took two steps, then wheeled about again.
    He didn’t dare to go back. For he was safely out. There was nothing that could persuade him—money or car or anything—to go back into the village.
    The light was waning and he headed northward, settling down to rolling up some distance—not running, but walking fast, with long, loose strides that ate up the very road.
    He