The Greek particle ē (ἦ) is an emphatic assertive particle meaning "surely, certainly, indeed, truly." It intensifies an assertion, expressing strong conviction or solemn affirmation. It appears rarely in the NT — its most striking use is Mark 8:12, where Jesus uses it in a solemn oath-like formula of refusal.
Mark 8:12 records Jesus sighing deeply in His spirit and saying, "Ē I say to you, no sign will be given to this generation." The particle functions like a solemn oath formula — "Truly I tell you" — expressing the absolute finality of His declaration. The Pharisees demanded a sign from heaven; Jesus sighs (the only place Mark records this sigh) and issues an emphatic, sweeping refusal. The generation that refuses to see what is before their eyes will receive no additional demonstration. The ē underscores the gravity: this is not a tentative position; it is settled, final, certain.