def probs(pct):
    """
    Return a human-readable string representing the probabilities.

    This scheme is shamelessly ripped from CIA's Words of Estimative
    Probability.

    https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/books-and-monographs/sherman-kent-and-the-board-of-national-estimates-collected-essays/6words.html

    100%                Certainty
    93%     +/- ~6%     Almost certain
    75%     +/- ~12%    Probable
    50%     +/- ~10%    Chances about even
    30%     +/- ~10%    Probably not
    7%      +/- ~5%     Almost certainly not
    0%                  Impossibility
    """
    pct = int(pct * 100)
    if pct == 100:
        return 'certain'
    if pct > 87:
        return 'almost certain'
    if pct > 63:
        return 'probable'
    if pct > 40:
        return 'about even'
    if pct > 20:
        return 'probably not'
    if pct > 2:
        return 'almost certainly not'
    return 'an impossibility'
