上句见：Day277
The Story of Philosophy《哲学的故事》第1章Plato第5节V. The Political Problem第1段第2句：

Justice would be simple matter, says Plato, if men were simple; an anarchist communism would suffice. For a moment he gives his imagination reign:
First, then, let us consider what will be their way of life…. Will they not produce corn, and wine, and clothes, and shoes, and build houses for themselves? And when they are housed they will work in summer commonly stripped and barefoot, but in winter substantially clothed and shod. They will feed on barley and wheat, baking the wheat and kneading the flour, making noble puddings and loaves; these they will serve up on a mat of reed or clean leaves, themselves reclining the while upon beds of yew or myrtle boughs. And they and their children will feast, drinking of the wine which they have made, wearing garlands on their heads, and having praises of the gods on their lips, living in sweet society, and having a care that their families do not exceed their means; for they will have an eye to poverty or war…. Of course they will have a relish — salt, and olives, and cheese, and onions, and cabbages or other country herbs which are fit for boiling; and we shall give them a dessert of figs, and pulse, and beans, and myrtleberries, and beechnuts which they will roast at the fire, drinking in moderation. And with such a diet they may be expected to live in peace to a good old age, and bequeath a similar life to their children after them (273).
浙江大学译本：他曾这样描绘过心中的理想国：

解析

1、 For a moment he gives his imagination reign:
片刻后，他就任由自己的想象驰骋了。
For a moment: destined to last for only a moment; during a moment 片刻；一会儿
Mr. Edgar was silent for a moment.艾加先生好一会儿没做声。《呼啸山庄》
give (one's) imagination reign：类似“give free reign to (one's) imagination”，表示“充分发挥某人的想象力；任由某人的想象力驰骋”。
Here — however serious life might be overall — one is allowed to play, to be tender and to give free reign to the imagination.在这个阶段——不管生活总体上是那么严肃——人还是可以玩耍，可以温柔，让想象力自由支配。《The school of Life》

片刻后，他就任由自己的想象驰骋了。

这句话写出了柏拉图基于人性简单而进行的畅想。