Four short lines are enough to move a whole household from laughter to loneliness. The speaker remembers a time when company made everyone "merry and good-natured," then turns to the present, where "alone" he is summoned to supper not by a person but by "a melancholy violin." The central idea is that a home is made of people more than of walls or routines. The house and the ritual of the evening meal stay the same, but without the others they change character completely.
The poem's structure is a simple hinge. It splits into two halves of two lines each, and each half opens with its key word: "Together" begins the first, "alone" begins the second. The semicolon at the end of line two is the pivot between them, a small pause in which the company disappears. There is no rhyme and no regular metre, so the effect depends on rhythm and line length. The first two lines move at an easy, conversational pace. The third is the longest, and its words ("melancholy violin") are slow and drawn out, like a bowed note left to hang. Then the fourth line shrinks to "called me to supper," which ends the poem on a plain, almost shrugging note. The poem gets quieter as it goes.
The "round house" is the poem's one piece of setting, and it is left open. The poem never says what kind of building this is, but a circle suggests something specific. A round space has no head, no corners and nowhere to hide, which fits a group sitting "together" and equal. Read that way, the same shape feels different once only one person is in it. That reading is an inference, but the poem rewards it, because it gives so little else to look at.
The language does more than it first appears to. Happiness is described in general, slightly old-fashioned labels: "merry and good-natured." These words sum up a mood rather than showing a scene, as if the speaker remembers the feeling but not the details. Sadness, by contrast, gets a sound. That imbalance is revealing: the good times are summarised, while the lonely present is vivid and immediate. "Melancholy" is also a transferred epithet. The feeling really belongs to the listener, but it is attached to the instrument, so the room itself seems to carry the mood. The poem also links its two states through sound. "Merry" and "melancholy" begin with the same letter, and "me" in the final line continues the pattern. It is as though the cheerful company and the sad solitude are variations on one note.
Grammar tells the same story. In the first half the speaker is part of an active "we" ("we were merry"). In the second half the speaker shrinks to "me," the object of someone else's verb, and the only thing that acts is the violin. The speaker has gone from taking part in a household to being called by one of its sounds. The poem never says whether the violin is really being played, remembered or imagined, and that ambiguity helps it. Whatever the source, the sound does the work a voice or a dinner bell would do.
Then there is "supper," the most ordinary word in the poem and perhaps the most painful. Supper is where a household gathers, so being called to it ought to mean company. The title sharpens the irony, since "Household" normally implies several people. Here it seems to name a place where only one person answers. The poem offers no explanation for why the others are gone, and it does not complain. It simply lets the reader notice the empty chairs.
That restraint is what makes the poem worth reading. It shows how much can be done with contrast, careful word placement and omission. It states no grief, only a change from "we" to "me," from merriment to a lone instrument, and trusts the reader to feel the distance between them.