Hebrew is a pretty predictable language, both in structure and meaning. When there is an exception, it is a whopper. And the biggest exception is the verb heh-yod-heh. What makes this particular verb so challenging is that we would probably consider it essential to human expression. It is the word for "to be."
When Shakespeare had Hamlet opine, "To be or not to be, that is the question," he might have been asking about the place of this verb in the Hebrew language. (All right, it's a long shot, but it's possible.) In fact, the present-tense active form of this verb almost never appears in Hebrew, Biblical, Rabbinic, Medieval or Modern. The words "is, "am," "are," which are ubiquitous in English, are understood in Hebrew. One does not say "I am speaking" in Hebrew; rather, one says "I speak," or perhaps, "I speaking." It is as if the word itself recognizes that there is no ability to capture the fluid moments of being.
The present-tense active of "to be" appears in two places you likely encounter. The first is in Hebrew grammar, where the present-tense is called, ironically, "hoveh," the form we rarely see in spoken or written text. The other is in the hymn "Adon Olam," in which the poet, describing God, has written "v'hu haya, v'hu hoveh, v'hu yi'h'yeh," (He was, He is, He will be). It is such an unusual usage that I would call it poetic license rather than syntactically correct.
Of course, just because we don't say the word doesn't imply that we don't need the word. And in its past and future forms (or perfect and imperfect, as they called in Biblical Hebrew), heh-yod-heh turns up a lot. "Was" and "will" are used to as liberally in Hebrew as they are in English. And the particular word in question is in a form of the future/imperfect called "jussive." Just to make this more complicated, English does not have a jussive form. We indicate the form by adding the words "let it" (or –him or –her) before the verb. So our word, "t'hi" (minus the "u," which means "and") turns out to translate as the title of one of the Beatles' last hits together: "let it be." (In fact, a Hebrew version of the song is entitled "Lu Y'hi.")
That's a long and complicated explanation for a small and simple word. But then, in a more accurate reading of Hamlet, to be or not to be requires a long and complicated explanation for all of us.