上句见：Day352
The Story of Philosophy《哲学的故事》第1章Plato第7节VI. The Psychological Solution第4段第5句：

But mere athletics and gymnastics would make a man too one-sided. "How shall we find a gentle nature which has also great courage? — for they seem to be inconsistent with each other"(375). We do not want a nation of prize-fighters and weight-lifters. Perhaps music will solve our problem: through music the soul learns harmony and rhythm, and even a disposition to justice; for "can he who is harmoniously constituted ever be unjust? Is not this, Glaucon, why musical training is so powerful, because rhythm and harmony find their way into the secret places of the soul, bearing grace in their movements and making the soul grateful?"(401; Protagoras, 326). Music moulds character, and therefore shares in determining social and political issues. "Damon tells me — and I can quite believe it —that when modes of music change, the fundamental laws of the state change with them."15
15Cf. Daniel O'Connell: "Let me write the songs of a nation, and I care not who makes its laws."
浙江大学译本：音乐塑造性格，进而在某种程度上决定着社会和政治事务。

解析

1、 Music moulds character, and therefore shares in determining social and political issues.
音乐塑造性格，因而一定程度上决定着社会及政治事务。
share in doing：有“参与做某事”“在做某事中起作用”，比较常见且地道。
Parent should share in educating their children.父母应该共同分担教育孩子的责任。

这句是对上句中音乐的总结，影响性格进而会左右社会及政治事务。and therefore有种进一步、更深入的结论。鉴于音乐的影响力如此巨大，所以对于音乐形式的选择就显得尤为重要。柏拉图的音乐选择观如何呢？在我的知识体系，他过于谨慎以至于限制音乐的形式。