Reference for Shevuot 8:4
ר"ע מאי טעמא קא מחייב לשעבר דדריש ריבויי ומיעוטי רבי נמי דריש ריבויי ומיעוטי
Concerning the laws of uncleanness, then, Rabbi has his own reason; but concerning oaths, where we do not find that he gives a reason of his own, how do we know [that he holds OATHS ARE TWO, SUBDIVIDED INTO FOUR]? - It is a reasonable assumption; for, what is R'Akiba's reason for including oaths in the past tense for liability? - Because he expounds 'amplifications and limitations'!<span class="x" onmousemove="('comment',' Infra 26a. R. Akiba expounds the verse (Lev. V, 4) thus: If any one swear clearly with his lips - 'amplification; (i.e., all oaths) ; to do evil or to do good - 'limitation' (i.e., this particularisation limits the general statement to oaths which are similar to the particular in that they are in the future tense) ; Whatsoever it be that a man utter clearly with an oath - another 'amplification' (this additional general statement serves to amplify the particular, adding even oaths which are not similar to it, i.e., even those in the past tense, and excluding only swearing to transgress a precept) .');"><sup>3</sup></span>