suspect, supposition, conjecture, guess, speculation, hypothesis, suspicion, guesswork, soupçon, sneaking suspicion, more...

certainty, conclusion, fact, reality

guess, conjecture, assumption, hypothesis, speculation, postulation, estimation, inference, deduction, more...

wild, mere, false, such, vague, first, only, reasonable, pure, shrewd, invincible

guess he,   can guess,   could guess