《列子·汤问》
另一把剑叫承影，在清晨天将亮的时候，或傍晚天将暗的时候，面向北观察它，淡淡地似乎有件东西存在着，但看不清它的形状。
二曰承影，将旦昧爽之交，日夕昏明之际，北面而察之，淡淡焉若有物存，莫识其状。
Another sword is called "Cheng Ying" (Mirage behind the shadow), at dawn or dusk, looking at it facing north, you will see it vaguely, but can't see the details.
<s>[INST] Identify the key themes in this Classical Chinese text and explain them in English: 二曰承影，将旦昧爽之交，日夕昏明之际，北面而察之，淡淡焉若有物存，莫识其状。 [/INST] Another sword is called "Cheng Ying" (Mirage behind the shadow), at dawn or dusk, looking at it facing north, you will see it vaguely, but can't see the details.</s>
Identify the key themes in this Classical Chinese text and explain them in English: 二曰承影，将旦昧爽之交，日夕昏明之际，北面而察之，淡淡焉若有物存，莫识其状。
user
Another sword is called "Cheng Ying" (Mirage behind the shadow), at dawn or dusk, looking at it facing north, you will see it vaguely, but can't see the details.
assistant