The Mouse (Symbol)
Though the mouse is a character, a conscious being with some degree of agency, the mouse is equally a symbol. This is because it takes on additional significance to the speaker, who imbues it with his own ideas about nature and power. He is all the more free to turn the mouse into a symbol because the mouse, of course, cannot speak, making it a kind of blank slate perfect for projecting meaning onto. For the speaker, the mouse symbolizes the natural world, especially the elements of nature that are weak, innocent, or vulnerable to exploitation by humans. As the poem delves into explorations of human intervention in the natural world, and into the broader differences between humans and nonhuman animals, the symbolism of the mouse becomes increasingly rich and complex, intertwining with its actual experiences as a character. For instance, the speaker notes with envy that the mouse can only think about the present and therefore, in a sense, has fewer worries—an observation that simultaneously allows readers to imagine the mouse's mental experience and cements its symbolic status as a simple, innocent being.
Agriculture (Motif)
It's no coincidence that the speaker discovers the mouse while plowing his fields. Agriculture has an ambivalent status in this poem. It's at once a process that seeks to control nature, and one that allows people like the speaker to survive. It dominates the life of the mouse, upsetting its nest and intruding on the natural world as a whole, but it also allows the mouse to eat by stealing the farmer's extra crops. And, finally, agriculture is presented as inextricable from humans' mental capacity, which the speaker is also uncomfortable with—he knows that his ability to plan and think abstractly lets him produce food and wealth, but he also knows that his intelligence opens him up to troubling thoughts emotions that the mouse doesn't share. Finally, in this poem agriculture sits beside a silent but implied parallel: industrialization. The invention of agriculture fundamentally reshaped the relationship between human beings and the natural world, while industrialization—a process in its nascent days during the publication of this poem— did the same.
