上句见：Day348
The Story of Philosophy《哲学的故事》第1章Plato第7节VI. The Psychological Solution第4段第1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, Glaucoma, 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：但是，单纯的竞技和体育运动只会使人太过片面。

解析

1、But mere athletics and gymnastics would make a man too one-sided.
但是，仅仅靠运动和体操会使人过于片面。
athletics: sports, games, and exercises that require strength and skill【不可数名词】体育运动
He came up to Oxford from Eton with a reputation for athletics and eccentricity.他从伊顿公演来到牛津，以运动和古怪著称。《魔法师》
gymnastics: physical exercises for developing strength and balance体操
He loved skiing and being outdoors. He studied bodybuilding, yoga, martial arts, and gymnastics.他喜欢滑雪和待在户外。他研读健身、瑜伽、武术和体操。《欧美人文风情》
one-sided: showing only one opinion or point of view片面的；偏颇的；不公正的 = biased
His book presents a somewhat one-sided view of the issue.他的书对这个问题的观点或多或少有些片面。

上段讲儿童的前期教育重点在身体锻炼上，这段马上以“But”指出其片面性。一个人仅靠运动及体操，可能就成为斯巴达一样的蛮人。柏拉图游历各国，还是取其长，补其短。