Answer:
The theme of the poem ‘A Day in Autumn’ by R.S Thomas is the transient nature of life and the inevitability of death. The speaker observes the beauty of the autumn landscape, but also recognizes the impermanence of it all. The leaves will fall, the flowers will wither, and winter will come. The poem emphasizes the idea that life is fleeting, and the inevitability of death hangs over everything. This theme is conveyed through the use of vivid and descriptive imagery, as well as the speaker's contemplative tone. The poem suggests that we should appreciate the beauty around us, but also be mindful of the fleeting nature of life and the inevitability of death.