The present study aims to investigate the various request constructions used in Classical Arabic and Modern Arabic language by identifying the differences in their usage in these two different genres. Also, the study attempts to trace the cases of felicitous and infelicitous requests in the Arabic language. Methodologically, the current study employs a web-based corpus tool (Sketch Engine) to analyze different corpora: the first one is Classical Arabic, represented by King Saud University Corpus of Classical Arabic, while the second is The Arabic Web Corpus “arTenTen” representing Modern Arabic. To do so, the study relies on felicity conditions to qualitatively interpret the quantitative data, i.e., following a mixed mode method. The findings of the present study show that request constructions vary in terms of occurrence between Classical Arabic and Modern Arabic. In Classical Arabic, (/laa/ لا) of prohibition is the most frequent construction, which is rarely used in the Web corpus where the command in the form of (/lam/لام + verb) is the most commonly emerging one, which is, in turn, seldom employed in the former corpus. The vocative (/ya/ يا) is the second most frequent construction in Classical Arabic, whilst the interrogative (/hel/ هل) emerged in the other genre. The third most common request construction is the interrogative (/hel/ هل) in Classical Arabic, but the vocative (/ya/ يا) is used in Modern Arabic. Nonetheless, some of these constructions fail to accomplish two or more conditions and hence are regarded as infelicitous requests. Such infelicitous constructions serve other functions than requests, such as negation, exclamation, and sarcasm.