Daf Yomi Moed Katan 14b -- Why No Mourning on a Festival?

Moed Katan 14b reads:

אבל אינו נוהג אבילותו ברגל שנאמר ושמחת בחגך

אי אבילות דמעיקרא היא אתי עשה דרבים ודחי עשה דיחיד
ואי אבילות דהשתא היא לא אתי עשה דיחיד ודחי עשה דרבים

A mourner does not conduct himself in mourning on the Festival.

For it is written {Devarim 16:14}

יד וְשָׂמַחְתָּ, בְּחַגֶּךָ: אַתָּה וּבִנְךָ וּבִתֶּךָ, וְעַבְדְּךָ וַאֲמָתֶךָ, וְהַלֵּוִי וְהַגֵּר וְהַיָּתוֹם וְהָאַלְמָנָה, אֲשֶׁר בִּשְׁעָרֶיךָ.

14 And thou shalt rejoice in thy feast, thou, and thy son, and thy daughter, and thy man-servant, and thy maid-servant, and the Levite, and the stranger, and the fatherless, and the widow, that are within thy gates.

If it is mourning from before {the Festival}, the positive commandment of the many comes and pushes off the positive commandment of the individual. And if it is the mourning of now {once the Festival has begun}, the positive commandment of the individual does not come and push off the positive commandment of the many.

Note that there is an abrupt transition in language from the first line to the second line. The first line is in Hebrew: אבל אינו נוהג אבילותו ברגל שנאמר ושמחת בחגך -- well, the pasuk is Hebrew of course, but we also have the word נוהג with the internal vav for present tense, which would not be present in Aramaic {they would use a kametz}, we have the ending of אבילותו with a vav rather than yud heh, another mark of Hebrew over Aramaic, the ש of שנאמר rather than a daled, and the nifal form of שנאמר, another mark of Hebrew.

In contrast, the rest of the statement is pure Aramaic.

אי אבילות דמעיקרא היא אתי עשה דרבים ודחי עשה דיחיד
ואי אבילות דהשתא היא לא אתי עשה דיחיד ודחי עשה דרבים
You have אי for "if," daled rather than shin in words like דמעיקרא דהשתא, דרבים , דיחיד, the kametz aleph ending in words like דמעיקרא and דהשתא, verbs like אתי where the root is Aramaic, and אתי and דחי which have Aramaic verb patterns. Thus, it is clearly Aramaic.

Why does this matter? Just because it is then an apparently later elaboration in Aramaic on an earlier Hebrew (possibly Tannaitic) statement.

I would suggest that rather than the reasoning supplied by the setama digmara in Aramaic above, there is a straightforward derasha going on:

אבל אינו נוהג אבילותו ברגל שנאמר ושמחת בחגך
For it is written {Devarim 16:14}

יד וְשָׂמַחְתָּ, בְּחַגֶּךָ: אַתָּה וּבִנְךָ וּבִתֶּךָ, וְעַבְדְּךָ וַאֲמָתֶךָ, וְהַלֵּוִי וְהַגֵּר וְהַיָּתוֹם וְהָאַלְמָנָה, אֲשֶׁר בִּשְׁעָרֶיךָ.

14 And thou shalt rejoice in thy feast, thou, and thy son, and thy daughter, and thy man-servant, and thy maid-servant, and the Levite, and the stranger, and the fatherless, and the widow, that are within thy gates.

Note how the mitzva is rejoicing in the Chag. And the pasuk ends וְהַיָּתוֹם וְהָאַלְמָנָה, "and the fatherless, and the widow." Thus, even those who are just now deprived of their relative have an obligation of וְשָׂמַחְתָּ בְּחַגֶּךָ.

Update: The above derasha I offered is unnecessarily complex and furthermore is false. I would suggest that the derasha is really as follows:

וְשָׂמַחְתָּ בְּחַגֶּךָ - And you shall rejoice in your Festivals, and not mourn in your Festivals.
Now who would I think would mourn in the Festival? Only a mourner. Thus, we have an explicit exclusion forbidding mourning during Festivals.

The whole give and take of the setama digmara does not read this derasha as an exclusion and as a derasha, but rather just takes it at face value, on the level of peshat. Thus, one has the standard commandment to rejoice, just as everyone else has. Therefore, the setama must resolve this generic positive commandment with the other general commandment for a mourner to mourn. And that is where I think the setama goes off in its explanation of the derivation of this law.