This poem presents a contrast between the month of May and y mis du ('the black month'). The proper name of the second month is not used in the poem, and there has been some uncertainty as to which of the three months of winter is meant. The editors of BDG chose to leave the matter open by entitling the poem 'Mawl i Fai a Dychanu y Mis Du' (CXVI). But in DGG (LI) the poem is given the title 'I Fis Mai ac i Fis Ionawr', and similarly in GDG (69) 'Mis Mai a Mis Ionawr', both following the manuscript title provided by David Johns in BM 29, 'i fis mai ac i fis Ionawr i ganmol mai a goganu Ionawr'. See further Thomas Parry's note, 'Y marwfis, y mis du', B ix (1937–9), 40–2, and also Melville Richards, 'Y mis du', B xiii (1948–50), 204–5. In fact y mis du is ambiguous, since it has been used in different regions of Wales to refer to all three winter months (see GPC 2465). December was sometimes called 'y mis du cyn y Nadolig' and January 'y mis du wedi'r Nadolig'. On the other hand, Myrddin Fardd says of November in Llên Gwerin Sir Gaernarfon (Caernarfon, 1908) 45, 'Y mis du y galwai yr hen bobl y mis hwn'. November is an miz du in both Breton and Cornish. Nevertheless, it is quite clear from the description in the poem itself, and particularly the reference to wind stripping the trees, that November is meant (as Edwards suggested, 1996, 276). Hail is mentioned, but not snow and ice as would be expected if January were being described. And the contrast between the first month of summer and the first month of winter, the two opposing poles of the year, is entirely logical.

The contrast is based on two contrasting personifications. May is a noble knight who conquers the land after defeating his enemy, rewarding his followers generously and dressing them in his green livery, whilst the 'black month' is a nasty destructive churl (cf. the similar personifications in 'Mawl i'r Haf' (35) and at the beginning of 'Y Cyffylog', 53.1–6). For examples of the same imagery in French literature see DGIA 277–8.