Midnight, darkness, and a sound: that is all Longfellow gives us at the start of this sonnet. The speaker doesn't watch the tide turn. He hears it. The sea "awoke at midnight from its sleep," and the verb makes the sea sound like something enormous opening its eyes. Everything in the first eight lines reaches us through the ear ("the first wave of the rising tide," "a voice," "a sound," "roar"), so we picture someone alone on a dark beach, unable to see how large the thing in front of him is.
The similes are interesting because they come from the land. The sound is "as of a cataract from the mountain's side, / Or roar of winds upon a wooded steep." To describe the sea, the speaker has to borrow waterfalls and storm-tossed trees, as though the noise were too big to belong to any one source. "Mysteriously multiplied" suggests it comes from every direction at once, and the repeated *m* sounds seem to echo. Even "a voice out of the silence of the deep" holds a paradox: a voice that rises from silence, with "deep" meaning both the sea and something further down.
The sound of the verse supports this. It is a Petrarchan sonnet, and its first eight lines use only two rhyme sounds: *sleep, sweep, deep, steep* and *wide, tide, multiplied, side*. The long vowels return again and again, like waves breaking on the same shore. The first sentence runs four lines without stopping, and the long word "uninterrupted" makes the line itself feel uninterrupted. The steady iambic pentameter works like a swell that keeps coming.
At line nine the poem turns: "So comes to us at times." The sea becomes a metaphor, and the vocabulary shifts from the concrete to the abstract. We now hear of "the unknown / And inaccessible solitudes of being," and the tide is renamed "the sea-tides of the soul." Look at the prefixes in these lines and in "uninterrupted" earlier: *un-*, *in-*. They point to things that cannot be reached or stopped. The rhymes loosen too. The sestet runs *unknown / own*, *being / foreseeing*, *soul / control*, so the tight echo of the octave gives way to something more open. Two of the rhymes, "being" and "foreseeing," are feminine, with an unstressed syllable trailing after the beat. These lines seem to drift past the edge of the metre, just as the thought drifts toward what it cannot grasp.
The central idea is about where inspiration comes from. Ideas feel like ours, but the poem hints otherwise. The phrase "that we deem our own" is gently deflating. We only *deem* them ours, and the poem suggests they are really "some divine foreshadowing and foreseeing / Of things beyond our reason or control." The comparison fits because the octave has already made us feel a sound arriving from nowhere, in the dark, without being asked for. When the sestet says thoughts arrive the same way, we recognise it. The final rhyme pairs "soul" with "control," and the poem has just argued that the two do not go together. Nobody commands a tide, and the soul's tides are no different.
Longfellow was one of the most widely read American poets of the nineteenth century, and this sonnet shows why his clear, musical verse lasted. In fourteen lines it turns an ordinary night-time experience into a claim about the mind and creativity, and the sea never stops being a sea along the way. The poem also doesn't pretend to explain the source of inspiration. Its words are "unknown," "inaccessible," "beyond." It ends in acceptance rather than an answer, and anyone who has had an idea arrive unbidden, late at night, will know the feeling.