Keats uses the poetic device of apostrophe in this poem. Apostrophe occurs when an inanimate object is addressed as if it is alive. Keats addresses the urn in the first stanza, calling it:

Thou still unravish'd bride of quietness,

Thou foster-child of silence and slow time

Keats also carefully structures the poem to reflect his rising emotion as he contemplates the urn and becomes more and more identified with it. The rise in emotion crescendos in the middle of the poem, in stanza three, as the speaker repeats the word "happy" over and over again, emphasizing his joy with the repeated use of exclamation points. After this high point, the speaker gradually comes down from his sense of euphoria.

Antithesis is another poetic device as the unchanging, eternal quality of the urn is continually contrasted to the fast changes of the natural world. One example is the speaker's delight that it will be forever spring on the urn:

Ah, happy, happy boughs! that cannot shed

Your leaves

There are numerous poetic techniques employed in "Ode on a Grecian Urn" by the Romanticist poet John Keats. Among these are elements of the sonnet form and rhyme, imagery, symbolism, alliteration, and personification.

Within the theme of how Art has the power to convey the truth of human experience, Keats uses several poetic devices:

• Personification

Addressing the urn as "bride of quietness" and "Sylvan historian," Keats gives human traits to the Grecian urn as he acknowledges that it contains a "flowery tale" that is sweeter than the poet's rhyme. Further, he comments, "Ah, happy, happy boughs!" 

• Imagery

In stanza I the poet describes the painting on the urn with its deities and mortals, maidens, and men. There is a "leaf-fringed legend," "pipes and timbrels." The urn depicts religious celebration and sexual play among other aspects of life. However, these images are frozen in time and the lovers will never kiss as they are arrested in their movements because they are painted on the urn.

In stanzas IV and V there is visual imagery with such descriptions as the "green altar," the heifer's "silken flanks with garlands," "river or seashore," the "red-breast," "a garden croft" and "gathering swallows."

• Alliteration

There is the repetition of the /th/ in line 18: "She cannot fade, though thou hast not thy bliss."

In another example, the /s/ is repeated in this line: "Will silent be; and not a soul to tell." And the /h/ is repeated throughout this line: "More happy love! more happy, happy love!"

• Symbolism

Employing the symbols of "trees" for Nature, "song" for Art, and "Bold Lover" for procreation, Keats explains the tension between what is on the urn and what is real. For the urn, "truth is beauty, beauty truth" (a literary device called chiasmus). This beauty lasts because it is frozen in time. However, for the poet who knows that beauty does not last, the truth is not restricted to the images on the urn. He realizes that the lovers will never consummate their love but will remain only in their moment.  

• "Sonnet" form

Keats uses iambic pentameter, and his poem resembles a sonnet as it is laid out on the page; however, there are only ten lines in each stanza. Still, the stanzas have a pattern to them as the rhyme scheme is nearly consistent throughout: The first four lines are ABAB, and the next six are CDE and then some variation of CDE (CED).

One poetic technique that is used in this poem from the outset is metaphor. The speaker compares the urn he is talking about to a series of different images that each point towards the centrality and importance of the urn as a symbol of eternal beauty. Note the comparisons that are established in the first couple of lines:

Thou still unravish'd bride of quietness,
     Thou foster-child of silence and slow time,
Sylvan historian, who canst thus express...

The urn is compared to a "still unravish'd bride of quietness," a "foster-child of silence and slow time" and a "Sylvian historian." These metaphors are very important in the way that they establish the sense of how this urn represents a transcendent beauty for Keats. For him, the urn is "unravish'd" in the sense that it stands for how true beauty and art does not diminish or fade over the years. True beauty dwells in a realm of "silence and slow time" that allows Keats to develop the contrast between the urn and the frail humans who are left to contemplate such beauty in their brief mortal spans. Therefore metaphor is one poetic technique that Keats uses with great effect in this poem.

Some poetic techniques used in "Ode on a Grecian Urn" include the following.

Apostrophe: Apostrophe in poetry is the address of someone who is not present or of a personified object. In this poem, the speaker addresses the urn—the personified object—they are looking at, calling it "thou" or you, and directly speaking to a figure on the urn, calling it "bold lover" and giving it advice. This technique underscores the speaker's sense of identification with the urn: he treats it and the scene he sees on it as if they are alive and can be interacted with.

Imagery: Imagery is description using any of the five senses of sight, sound, touch, taste, or smell. The poem abounds in imagery as the speaker describes the scene of the urn. For example, we can see and hear in our imaginations the priest leading the young cow that is decorated with flowers and "lowing" out of town.

Alliteration: Keats employs alliteration in the poem, creating a pleasing sense of rhythm, which can be seen in the following line:

Of marble men and maidens overwrought.

Rhetorical questions: Keats also uses a series of rhetorical questions in the poem, questions that are not meant to be answered but which aid in offering a quick thumbnail description of the urn, such as in "What pipes and timbrels?" These questions also reveal the speaker's curious and wondering state of mind.

Finally, "Ode on a Grecian Urn" is a lyrical or emotional poem, and Keats highlights the deep emotions the speaker is feeling through his repetition of words like "happy" and the use of exclamation points.