Understanding 「自信があれば半ば成功したも同然だ。」

Question

In

自信があれば半ば成功したも同然だ。

Confidence is half the battle. (Idiomatic translation)

I'm having trouble getting to the idiomatic translation.

It seems like a good literal translation of the clause before も is:

自信があれば半ば成功した

If one has self-confidence, one does success halfly.

1. What role is も playing? Translating it as "too" or "also" seems a bit awkward to me (i.e. "if one has self-confidence, one does success halfly too" is a bit weird?).

2. What is the 同然だ doing at the end? Does it mean something like: "it is natural", so that the overall sentence becomes: "it is natural that if one has self-confidence, one does success halfly"?

Answer 1

～も同然だ should be learned as a set phrase, but to break down,

• This も is yet another example of exclamatory-も. Here it's close to "even".
• 同然 is a noun (no-adjective) meaning "virtually/effectively the same".

So 半ば成功したも同然だ means (事実上)半ば成功したのと同じだ, or "(It's even) virtually the same as having half-succeeded."

In this pattern, a nominalizer is usually not present after the verb because of this, but you may occasionally see an explicit の (e.g., 成功したのも同然だ).