In later years he relaxed some of the formality of his work, losing the rhymes and strict metricality but always strove to maintain the lucidity. He became a free verse poet with the publication of "Surroundings" in 1966. Seamus Heaney described his work as "an ongoing education in the marvellous possibilities of lyric poetry." Ted Hughes wrote, "whenever I meet his poems, I'm always struck by their undated freshness, everything about them is alive, as new and essential, as ever." Another poet, beside Donne, whom MacCaig claimed was a great influence on his work was Louis MacNeice. Although he never lost his sense of humour, much of his very late work, following the death of his wife in 1990, is more sombre in tone. The poems appear to be full of heartbreak but they never become pessimistic.