The Nightingale (symbol)
The titular nightingale refers to the story of Tereus and Philomela that was featured in Metamorphoses by the Latin poet Ovid. Ovid's story recalls the rape of Philomela by Tereus, and her eventual transformation into a nightingale. This is represented in Sidney's poem in the line "for Tereus’ force on her chaste will prevailing." Sidney documents her laments and cries of pain. These cries are symbolic of the wrongs that were done against her by Tereus.
April (symbol)
April is traditionally seen as the first month of Spring. With Spring comes new life, greenery, and an escape from winter's pains. In "The Nightingale," the titular character arrives "as soon as April bringeth." For the nightingale, spring also marks the beginning of the healing process; the speaker tells her that her "earth now springs" as the world around her bursts into bloom. Spring, however, does not bring a cure for the speaker's woes; his earth "fadeth." This suggests that his pain is beyond the healing and restorative powers of the natural world.
The Thorn (symbol)
The thorn is the representation of both the speaker and the nightingale's sorrow. It is first mentioned in the third line of the poem, when speaking of the cries of the nightingale and "a thorn of her song-book making." It is then repeated in the final line of both stanzas, "thy thorn without, my thorn my heart invadeth." Here the speaker expresses his belief that the nightingale is able to express and show her pain, as her thorn is "without" (outside). In contrast, he is unable to express his pain; his thorn is "within," where it hurts all the more. He goes on to say that in fact invades his heart. The thorn also falls in line with the spring-time setting, as thorn-bearing plants grow in spring. In other words, the speaker's pains only expand in the spring.
Singing (motif)
As a nightingale, Philomela is only able to express herself through song ("her throat in tune expresseth"). Singing is typically associated with beauty and purity, but in the case of the nightingale it is a representation of pain, suffering, "and mournful bewailing." Yet because she can only express herself through (wordless) song, she is not able to truly impart the horrible nature of her situation. She was raped by Tereus and turned into a bird, and her only outlet is singing. Nonetheless, the speaker suggests "that here is juster cause of plaintful sadness" his own inability to express himself in song. Here another gendered reading can be taken. While women are offered more latitude to express their emotions, these emotions are often belittled and ignored.
Tereus (symbol)
Tereus is representative of the source and suffering. Yet he holds a dynamic position in the poem. In the first stanza it is written, "for Tereus’ force on her chaste will prevailing." This directly suggests the rape ("force") committed against Philomela. In the second stanza, however, the sentiment shifts. The speaker claims, "but Tereus’ love, on her by strong hand wroken." Phrasing Tereus' rape of Philomela as "love" is peculiar and problematic. By doing so, the speaker is able to prioritize his own worries above Philomela's. In this sense, he uses Tereus to reduce the plight of Philomela so as to aggrandize his own position.
