~ばいい for suggestions

Question

I am aware that ~ばいい can be used to suggest or imply something. For example, in the sentence:

自分ですればいいだろ (Do your own work)

However, I tried to make the sentence: Come with her to the party / It is good that you come with her to the party

彼女とパーティに行けばいいですね

But I was told that this sounds unnatural, and I should therefore say:

彼女とパーティに行けるといいですね (another conditional!)

My questions:

• Any conditional can be used for generating this suggestions?

• Is there any rule so that we know which conditional should we use in each case? Because I don't understand why my sentence is unnatural.

Answer 1

(First, the Japanese verb for "come" is "来る" not "行く", but for now we'll pretend that "go(行く)" is our verb.)

"彼女とパーティに行けばいいですね。" sounds unnatural because you used the wrong discourse particle "ね" at the end. (It's not wrong-wrong, actually, but... unnatural, if only for the nuance you are trying to convey.) For the function of "ね", see Yuuichi Tam's answer.

The right choice would be "よ" or not to use any at all. (The nuance varies between with and without it, but not too greatly.) Apart from that, your sentence is perfectly fine:

彼女とパーティに行けばいいです(よ)。 ("It will be good if you go to the party with her." Or less literally, "You should go to the party with her.")

Whoever told you to rewrite it as "彼女とパーティに行けるといいですね。" slyly converted the verb to the potential form (行ける: can go), along with the ば→と change. As a result something more than a little nuance was altered. Namely, the sentence turned from a suggestion/advice to an expression of hope!:

彼女とパーティに行けるといいですね。 ("It will be good if you can go to the party with her." Or less literally, "I hope you can go to the party with her.")

The difference in meaning is due to the change not in the conditional word (ば→と) but rather in the verb form. (And look what an impact it makes on the semantics of the whole sentence!)

You can replicate the same change in meaning without swapping the conditional word. You need only to change the verb form to the potential (and the discourse particle to "ね"):

(1a) 彼女とパーティに行けばいいです(よ)。 (You should go to the party with her.)
(1b) 彼女とパーティに行ければいいですね。 (I hope you can go to the party with her.)

(2a) 彼女とパーティに行くといいです(よ)。 (You should go to the party with her.)
(2b) 彼女とパーティに行けるといいですね。 (I hope you can go to the party with her.)

Answer 2

Because this ね is used as expectation for the agreement and reply like そろそろ出かけようね.

彼女とパーティに行けばいい means you should go to the party with her and this sentence is a suggestion, so this sentence added ね is unnatural because speaker doesn't expect the agreement and reply.

彼女とパーティに行けるといい means I hope you can go to the party with her and this sentence added ね is natural because speaker expects the agreement and reply.