A.T. Robertson Commentary John 8:55

"and ye have not known him: but I know him; and if I should say, I know him not, I shall be like unto you, a liar: but I know him, and keep his word." — John 8:55 (ASV)

And ye have not known him (κα ουκ εγνωκατε αυτον). Adversative use again of κα="and yet." Perfect active indicative of γινωσκω, the verb for experiential knowledge. This was true of the κοσμος (1:10; 17:25) and of the hostile Jews (16:3). Jesus prays that the world may know (17:23) and the handful of disciples had come to know (17:25).

But I know him (εγω δε οιδα αυτον). Equipped by eternal fellowship to reveal the Father (1:1-18). This peculiar intimate knowledge Jesus had already claimed (7:29). Jesus used οιδα (8:19; 15:21) or γινωσκω (17:23,25) for the knowledge of the Father. No undue distinction can be drawn here.

And if I should say (καν ειπω). Third-class condition (concession), "even if I say," with κα εαν (καν) and second aorist active subjunctive. "Suppose I say."

I shall be like you a liar (εσομα ομοιος υμιν ψευστης). Apodosis of the condition. Hομοιος (like) is followed by the associative-instrumental case υμιν. The word ψευστης (liar), in spite of the statement that they are the children of the devil, the father of lying (8:44), comes with a sudden jolt because it is a direct charge. This word liar is not considered polite today in public speech when hurled at definite individuals. There is a rather free use of the word in 1 John 2:4,22; 4:20; 5:10. It is not hard to imagine the quick anger of these Pharisees.