杜甫七言律詩成就高邁，甚至無與倫比，幾乎已成論者共識。其中核心特色在於「悲壯」──人的主觀意志不能克服外在客觀命運，因而有悲；而且意志如果持續抵抗，不僅適得其反，更加深化悲哀，最後甚至逼出壯烈之感。悲壯必須透過兩種力量的衝突而產生。杜甫七律悲壯之感成因在於：杜甫人生際遇呈現對立狀況──極盛開元之治以及極衰安史之亂都曾親歷；律詩格律處處呈現對立設計──平仄和對仗，正好適合用來呈現衝突對立之情。本文因而認為杜甫七律悲壯特色成因在於：杜甫本身具有強大衝突之感，而且他在相對適合表達對立之情的文體──七律之中，將此種情感發揮得淋漓盡致。最後，則以杜甫七律名篇〈秋興〉八首證成此種說法，並且指出〈秋興〉八首其實演示宇宙生成變化之理，在在顯示杜甫詩歌藝術已達化境。

That the achievement of Du Fu’s seven-character octave is outstandingly incomparable has almost become a common consensus of the scholars in this field. The core features of Du Fu’s seven-character octave would be “sorrow and solemnity”— a human’s subjective will could not overcome the exterior and objective “grand” fate, and thus “sorrow comes”. And if one’s will keeps resisting, that would not only cause the opposite reaction, but also deepen the “sorrow”, forcing the heroic sense to come out in the end as well. The senses of “sorrow and solemnity” in Du Fu’s seven-character octave is obvious, the reason is that sorrow and solemnity must be produced through the conflict of two powers. The design of opposition is presented everywhere in the seven-character octave’s meters— the tone pattern and the couplets are suitable to be used exactly for presenting the status of conflict and opposition. In addition, Du Fu’s life experience seems to demonstrate a similar condition of opposition— he personally experienced the most prosperous period, the flourishing Kai-yuan Reign Period, and the weakest one, An Shi Rebellion. Therefore, Du Fu’s senses and feelings of “sorrow and solemnity” seem to be more substantial, natural and powerful. I would thus argue in this paper that the cause to form the features of Du Fu’s seven-character octave “sorrow and solemnity” is that Du Fu himself had possessed the strong feelings of powerful conflict. He had this kind of feeling most beautifully described in the literary form of seven-character octave, which is relatively suitable to express the condition of opposition. At the end of this paper, I would prove my argument with Du Fu’s famous works— the eight poems of Autumn Association.