Do Not Go Gentle into That Good Night by Dylan Thomas begins with Thomas's plea to his father to be strong and to fight death. Death is not something to be taken lightly and so Thomas uses the structure of a villanelle (the form of the poem, a so-called "pastoral lyric") to express his message most intensely. The villanelle is nineteen lines long and the first five stanzas are only three lines in lengths followed by one quatrain to complete the poem.
Iambic pentameter features in Thomas's poem, creating the familiar "Dadum, dadum..." rhythm where the second syllable is stressed. However, Thomas did not like to be conventional so the rhythm is not strictly adhered to in terms of metric feet but rather in terms of there being ten syllables per line.
Old age should burn and rave at close of day
The rhyme scheme is constructed around the words "day" and "night," and words which rhyme with them. The repetition of the third lines, such as " Rage, rage against the dying of the light" and the fact that the rhyme comes from the same two words, give an added rhythm to the poem other than that created by syllables and there is an insistence created through this rhythm, allowing Thomas to get his message across.