Is וּכְתַבְתָּ֛ם in Shema with Shva Na or Shva Nach

Question

My daughter goes to a chabad school (nusach ari?) and has been taught in class that וּכְתַבְתָּ֛ם in the shema (end of first paragraph) is with a shvah na on the כְ. She also says it has the asterisk ontop of the chaf in her siddur.

However, I have only seen it in the siddurim (ashkenaz) with a shva nach (silent).

Is there a difference with this pronunciation between the different nusachot?

Answer 1

Short answer (as JoelK noted, see this one for more) -- disagreement among grammarians about cases like this. Listen to your favorite baal kriah read Exodus 7:29, about the frogs:

וּבְכָה וּבְעַמְּךָ, וּבְכָל-עֲבָדֶיךָ

All three of those "vet"s are in that same gray zone.

As it was taught to me -- you can't start a word with two sh'vas, as you'd have a conflict between "first letter is always na" and "two sh'vas together? Second is na" So "v'b'cha" became "uvcha." However it would have been "b'cha", so some retain the na.

Answer 2

The problem is based on the problem of whether the vav-hachibur that is marked with a shuruk and pronounced like "oo" in look is really a kubutz or a shuruk. Since kubutz is (according to R' Eliyahu Bachur) 'A movement between a shuruk and a chirik' and a t'nuaa k'tana (small movement) the rule will apply that if it's not emphasised a sh'va after it will be nach, and vise versa with a t'nua g'dola like shuruk, where it will be na. The general consensus though is that the vav-hachibur shuruk is a shuruk, so, unless the vav itself is emphasised, the sh'va after it will be na and not nach.