这句体现了“感官只能看到表象，惟有理性才能把握本质及规律”。“greet our senses”生动写出了表象及细节对我们感官的冲击，与后面的“unperceived”形成了巨大的反差。正如看东西与观察东西这两件事，前者几乎人人都会，但后者却是鲜有人会。

Behind the surface phenomena and particulars which greet our senses, are generalizations, regularities, and directions of development, unperceived by sensation but conceived by reason and thought.
在那些冲击我们感官的表面现象和种种细节的背后，存在着概括、规律以及发展趋势。而这些无法被感官所感知，却能由理性及思维所理领会。

细节解析

1、particulars：facts or details about something are written down or kept as records细节；
The nurses at the admission desk asked her for particulars.住院接待处的护士向她询问了详细情况。
2、 unperceived：without being noticed, unnoticed, unobserved未察觉到
I could see what are going on around me, while wholly unperceived myself.我能看见周边所发生的一切，却对自己毫无察觉。《为奴十二年》
3、conceived：to think or create (something) in the mind构想，想象
I cannot conceive anything which will cover the facts, I answered.《福尔摩斯四签名》

所在段落

The Story of Philosophy《哲学的故事》第1章Plato第7节VI. The Psychological Solution第14段第4句：

But this famous doctrine of Ideas, embellished and obscured by the fancy and poetry of Plato, is a discouraging maze to the modern student, and must have offered another severe test to the survivors of many siftings. The Idea of thing might be the "general idea" of the class to which it belongs (the Idea of John, or Dick, or Harry, is Man); or it might be the law or laws according to which the thing operates (the Idea of John would be the reduction of all his behavior to "natural laws"); or it might be the perfect purpose and ideal towards which the thing and its class may develop (the Idea of John is the John of Utopia). Very probably the Idea is all of these — idea, law and ideal. Behind the surface phenomena and particulars which greet our senses, are generalizations, regularities, and directions of development, unperceived by sensation but conceived by reason and thought. These ideas, laws and ideals are more permanent — and therefore more "real" — than the sense-perceived particular things through which we conceive and deduce them: Man is more permanent than Tom, or Dick, or Harry; this circle is born with the movement of my pencil and dies under the attrition of my eraser, but the conception Circle goes on forever. This tree stands, and that tree falls; but the laws which determine what bodies shall fall, and when, and how, were without beginning, are now, and ever shall be, without end. There is, as the gentle Spinoza would say, a world of things perceived by sense, and a world of laws inferred by thought; we do not see the law of inverse squares but it is there, and everywhere; it was before anything began, and will survive when all the world of things is a finished tale. Here is a bridge: the sense perceives concrete and iron to a hundred million tons; but the mathematician sees, with the mind's eye, the daring and delicate adjustment of all this mass of material to the laws of mechanics and mathematics and engineering, those laws according to which all good bridges that are made must be made; if the mathematician be also a poet, he will see these laws upholding the bridge; if the laws were violated the bridge would collapse into the stream beneath; the laws are the God that holds up the bridge in the hollow of his hand. Aristotle hints something of this when he says that by Ideas Plato meant what Pythagoras meant by "number" when he taught that this is a world of numbers (meaning presumably that the world is ruled by mathematical constancies and regularities). Plutarch tells us that according to Plato "God always geometries"; or, as Spinoza puts the same thought, God and the universal laws of structure and operation are one and the same reality. To Plato, as to Bertrand Russell, mathematics is therefore the indispensable prelude to philosophy, and its highest form; over the doors of his Academy Plato placed, Dantesquely, these words, "Let no man ignorant of geometry enter here."16
16The details of the argument for the interpretation here given of the doctrine of Ideas may be followed in D.G. Ritchie's Plato, Edinburgh, 1902, especially pp.49 and 85.
浙江大学译本： 我们每日面对的现象和个案背后，是无法为感官所知、只理智和思想去领悟的规律、规则和发展方向。

上句见：Day413