《詩經》周南關雎篇，為詩經之首，歌詠愛情，文辭優美，音律和諧，意涵情味雋永，扣人心弦，傳頌千年，成為中國詩歌抒情傳統的濫觴。《論語、八佾篇》：子曰：「〈關雎〉樂而不淫，哀而不傷。」得溫柔敦厚之詩教也。第三章詩句中云：「求之不得，寤寐思服。悠哉悠哉，輾轉反側。」其中「思服」兩字，語意上最為模糊，成為歷來學者解說重點，但是尚有商議之處。本文試從《詩經》中相同之用字、用法、上下文義、文句之間的關係、用字本義或不同情況下的使用，作一分析推論，以明其義。

“Guan Jiu” is the first poem in the Book of Odes. It begins by describing a lover's grief at being separated from his lover and ends by describing their joyful union. Among ancient classical works, scholars place special value on its strength in excellent language as well as rhythmic harmony. For thousands of years, the pleasure and enrichment in "love" it conveyed has made “Guan Jiu” the model of Chinese lyrical poems. In Confuciam Analects, Confucius said, "Guan Jiu allows for pleasure without being lewd and allows for grief without being too painful." The poem provides moral teachings and the intellectual stimulation. In the third stanza, James Legge tranlates as follows; He sought her and found her not, And waking and sleeping he thought about her. Long he thought; long and anxiously; On his side, on his back, he turned, and back again. Many scholars held different opinions on the two charactors, "si" and "fu" in the third line (寤寐思服) for their ambiguous meanings. There are still rooms for discussion. This article is intended to analyze these two charactors on their application in the context of a sentence and their different expressions in the Book of Odes.