杜甫與李商隱，是唐人七律中最具代表性的兩家，昔人常說李商隱七律師法杜甫，並非無見。不過，如果從吟詠聲情這一點來看，兩家七律實存有極大差異。杜甫七律，從一句到一篇，其字音的高低長短洪細，在口腔中產生很多變化，往往愛用大開大合之法。李商隱七律，口腔開合度比較小，他喜歡讓字音在窄小的口形中，纏綿吟揉。因此，兩家在聲情表現上，面目截然不同。本文旨在舉例說明這種現象，指出兩家七律的根本不同在那裡。如果在現場，叫任何一個人大聲讀出來，或者曼聲長吟，立即可以判別。可惜論文必須借用文字，使用文字又必須借用中古音的擬音，才能逐字分析發音結構，實在是不得已的。讀本文者，希望不要拘泥文字，直接用自己的口腔脣舌，去揣摹文中所說的現象，庶幾可以得之。

Du Fu and Li Shangyin are two of the most representative poets writing Seven-Character Regulared Verses. Critics in the past used to think that the later learned from the former, but if regarding the practice of reciting and emotional expression, the two poets are fundamentally different. Reciting Du Fu’s poems, one needs to pay special attentions to the tone and pitch and dramatically move the mouth; while reciting Li Shangyin, one needs not open and close the mouth so widely because he would have the sounds vibrate in the closed space. Therefore, the two peots’ expressions of sounds are fundamentally different. The present article aims to take examples to explain such a difference. While reciting the poems, anyone can easily tell the difference; but in writing, one has to borrow ancient words of onomatopoeia. Thus it is necessary to analyze the linguistic structure. Meanwhile, readers can only sense the difference while actually reciting the poems.