How was 手伝わなあかん conjugated?

Question

I was wondering how 手伝わなあかん was conjugated. I know that it consists of the words 手伝う and あかん but I don't know why the い was dropped. Is it slang?

Answer 1

This な is a Kansai-ben contracted version of ねば, which is an (archaic/literary) negative-hypothetical verb ending (≒"if not").

近畿方言#否定

仮定形は「ね」であるが、後続の助詞「ば」と融合して「な」や「ん」となる（例：行かねばあかん→行かなあかん、行かねばならん→行かなならん・行かんならん）。

• 手伝う: to help/assist
• 手伝わぬ: not to help (archaic negative form)
• 手伝わねば: if not help (archaic negative-hypothetical form)
• 手伝わな: if not help (Kansai-ben contraction of 手伝わねば)

So your sentence is 手伝わねばならない or 手伝わないといけない in standard Japanese.

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• あかん is originally 明かぬ, but it means "sucks" or "is bad" in Kansai-ben. See this question.
• Just like ねば/ないと in standard Japanese, な in Kansai-ben can mean "must" on its own.

  もう行かないと。= もう行かねば。= もう行かな。= It's time to go.

• ねば can contract also to にゃ or にゃあ in many dialects in middle/western Japan.

  手伝わなにゃならん。 = 手伝わないといけない。 = I must help them.