"Or if he touches the uncleanness of a man" (Leviticus 5:3). "A man" - this refers to a corpse. "The uncleanness of a man" - this is the uncleanness of the dead. "Of any uncleanness of his" comes to include those with a flux, women with a flux, menstruants, and women after childbirth. I have learned only the grave [longer-lasting] days; from where do I learn the lighter days? Scripture teaches, saying "of any uncleanness of his." "By which he may be defiled" comes to include one who lies with a menstruant. "By it" comes to include one who swallows the carcass of a clean bird. If the lighter cases were stated, why were the graver cases stated? For had the lighter cases been stated and not the graver ones, I would have said: for the lighter cases one brings a sliding-scale offering, but for the graver ones a fixed offering. And had the graver cases been stated and not the lighter ones, I would have said: for the graver cases one is liable, but for the lighter ones one is exempt. Therefore it is necessary to state the graver cases and necessary to state the lighter cases.
Corpse Defilement and the Many Forms of Ritual Impurity
Yalkut Shimoni on Torah 471:7
אוֹ כִי יִגַּע בְּטֻמְאַת אָדָם. אָדָם, זֶה הַמֵּת. טֻמְאַת אָדָם, זֶה טֻמְאַת מֵת. לְכָל טֻמְאָתוֹ, לְרַבּוֹת זָבִים וְזָבוֹת נִדּוֹת וְיוֹלְדוֹת. אֵין לִי אֶלָּא יְמֵי חֲמוּרִים יְמֵי קַלִּים מִנַּיִן, תַּלְמוּד לוֹמַר "לְכֹל טֻמְאָתוֹ". "אֲשֶׁר יִטְמָא", לְרַבּוֹת בּוֹעֵל נִדָּה. בָּהּ, לְרַבּוֹת אֶת הַבּוֹלֵעַ נִבְלַת עוֹף טָהוֹר. אִם נֶאֶמְרוּ קַלּוֹת לָמָּה נֶאֶמְרוּ חֲמוּרוֹת, שֶׁאִלּוּ נֶאֶמְרוּ קַלּוֹת וְלֹא נֶאֶמְרוּ חֲמוּרוֹת הָיִיתִי אוֹמֵר עַל הַקַּלּוֹת בְּעוֹלֶה וְיוֹרֵד עַל הַחֲמוּרוֹת קָבוּעַ, אִם נֶאֶמְרוּ חֲמוּרוֹת וְלֹא נֶאֶמְרוּ קַלּוֹת הָיִיתִי אוֹמֵר עַל הַחֲמוּרוֹת הוּא חַיָּב עַל הַקַּלּוֹת הוּא פָּטוּר, צָרִיךְ לוֹמַר חֲמוּרוֹת וְצָרִיךְ לוֹמַר קַלּוֹת.