It should allow prediction.

它能让我们做预测
You should be able to say how will these atoms react;

我们能用它预知原子的运作
how will this molecule react;

分子又会发生什么反应
what valence should nitrogen have;

氮是几价
how can it be both pentavalent and trivalent?

为何它时而三价时而五价
A little below this on the scale of desirability is suggestion.

退一步说这理论起码能给我们暗示
A theory may -- even if it doesn't give you the proper thing,

即时它不能确凿地告诉你什么
may at least suggest some experiment that would be really good to do.

至少能暗示你做些有用的实验
Below that is explanation--

再退一步说它要能给出解释
according to my theory all these known facts fit together,

能用这个理论把现有的一切都说通
but who knows about any new thing.

但以后发生的事就管不着了
And lowest is classification and remembering;

一个理论的底线功能是分类与记忆