The sonnet begins with the poet's apparent acknowledgment of the compelling quality of the emotional union of "true minds". As Helen Vendler has observed, “This famous almost ‘impersonal’ sonnet on the marriage of true minds has usually been read as a definition of true love.” This is not a unique theme of Shakespeare’s sonnets. Carol Neely observes that “Like [sonnet] 94, it defines and redefines its subject in each quatrain and this subject becomes increasingly concrete, attractive and vulnerable.” Shakespeare tends to use negation to define love according to Lukas Erne, “The first and the third [quatrains], it is true, define love negatively: 'love is not...'; Love's not...'. The two quatrains are further tied together by the reappearance of the verbs 'to bend' and 'to alter'.” Love is defined in vague terms in the first quatrain.
Garry Murphy observes that the meaning shifts with the distribution of emphasis. He suggests that in the first line the stress should properly be on "me": “Let ME not to the marriage of true minds...”; the sonnet then becomes “not just a gentle metaphoric definition but an agitated protest born out of fear of loss and merely conveyed by means of definition.” C.R. B. Combellack disputes the emphasis placed on the “ME” due to the “absence from the sonnet of another person to stand in contrast. No one else is addressed, described, named, or mentioned.”  Murphy also claims that “The unstopped first and second lines suggest urgency in speech, not leisurely meditation.” He writes that the short words when delivered would have the effect of “rapid delivery” rather than “slow rumination”. Combellack questions this analysis by asking whether “urgency is not more likely to be expressed in short bursts of speech?” He argues that the words in the sonnet are not intended to be read quickly and that this is simply Murphy’s subjective opinion of the quatrain. Murphy believes the best support of the “sonnet itself being an exclamation” comes from the “O no” which he claims a person would not say without some agitation. Combellack observes that “O no” could be used rather calmly in a statement such as “O no, thank you, but my coffee limit is two cups.” If anything, Combellack suggests, the use of the “O” softens the statement and it would require the use of different grammar to suggest that the sonnet should be understood as rapid speech.
The poetic language leaves the sort of love described somewhat indeterminate; “The 'marriage of true minds' like the 'power to hurt' is troublesomely vague open to a variety of interpretations.” Interpretations include the potential for religious imagery and the love being for God, “Lines one and two echo the Anglican marriage service from the Book of Common Prayer.” The concept of the marriage of true minds is thought to be a highly Christian; according to Erne, “The mental picture thus called up in our minds of the bride and bridegroom standing up front in a church is even reinforced by the insistence on the word alter/altar in the following line.”
The second quatrain explains how love is unchanging according to Neely, “Love is a star, remote, immovable, self-contained, and perhaps, like the 'lords and owners of their faces,' improbably and even somewhat unpleasantly cold and distant.”  The second quatrain continues Shakespeare's attempt to define love, but in a more direct way. Shakespeare mentions “it” in the second quatrain according to Douglas Trevor, “The constancy of love in sonnet 116, the “it” of line five of the poem, is also – for the poet – the poetry, the object of love itself.”  Not only is there a direct address to love itself, the style Shakespeare’s contemplation becomes more direct. Erne states, “Lines five to eight stand in contrast to their adjacent quatrains, and they have their special importance by saying what love is rather than what it is not.” This represents a change in Shakespeare's view that love is completely undefinable. This concept of unchanging love is focused in the statement, “'[love] is an ever-fixed mark'. This has generally been understood as a sea mark or a beacon.”  This concept may also convey in a theological sense. During the Reformation there was dispute about Catholic doctrines, “One of the points of disagreement was precisely that the Reformers rejected the existence of an ever-fixed, or in theological idiom, 'idelible' mark which three of the sacraments, according to Catholic teaching, imprint on the soul.” This interpretation makes God the focus of the sonnet as opposed to the typical concept of love.
The compass is also considered an important symbol in the first part of the poem. John Doebler identifies a compass as a symbol that drives the poem, “The first quatrain of this sonnet makes implied use of the compass emblem, a commonplace symbol for constancy during the period in which Shakespeare's sonnets were composed.”  Doebler identifies certain images in the poem with a compass, “In the Renaissance the compass is usually associated with the making of a circle, the ancient symbol of eternity, but in sonnet 116 the emphasis is more upon the contrasting symbolism of the legs of the compass.”  The two feet of the compass represent the differences between permanent aspects of love and temporary ones. These differences are explained as, “The physical lovers are caught in a changing world of time, but they are stabilized by spiritual love, which exists in a constant world of eternal ideals.”  The sonnet uses imagery like this create a more clear concept of love in the speaker's mind.
In the third quatrain, “The remover who bends turns out to be the grim reaper, Time, with his bending sickle. What alters are Time’s brief hours and weeks…” and “Only the Day of Judgment (invoked from the sacramental liturgy of marriage) is the proper measure of love’s time””  The young man holds the value of beauty over that of love. When he comes to face the fact that the love he felt has changed and become less intense and, in fact, less felt, he changes his mind about this person he’d loved before because what he had felt in his heart wasn’t true. That the object of his affection’s beauty fell to “Time’s Sickle” would not make his feelings change. This fact is supported by Helen Vendler as she wrote, “The second refutational passage, in the third quatrain, proposes indirectly a valuable alternative law, one approved by the poet-speaker, which we may label “the law of inverse constancy”: the more inconstant are time’s alterations (one an hour, one a week), the more constant is love’s endurance, even to the edge of doom”  Vendler believes that if the love the young man felt was real it would still be there after the object of that love’s beauty had long faded away, but he “has announced the waning of his own attachment to the speaker, dissolving the “marriage of true minds””  Shakespeare is arguing that if love is true it will stand against all tests of time and adversity, no manner of insignificant details such as the person’s beauty fading could alter or dissolve “the marriage of two minds”.
The couplet of Sonnet 116 Shakespeare went about explaining in the inverse. He says the opposite of what it would be natural to say about love. For instance, instead of writing something to the effect of ‘I have written and men have loved,’ according to Nelson, Shakespeare chose to write, “I never writ, nor no man ever loved.” Nelson argues that “The existence of the poem itself gives good evidence that the poet has written. It is harder to see, however, how the mere existence of the poem could show that men have loved. In part, whether men have loved depends upon just what love is…Since the poem is concerned with the nature of love, there is a sense in which what the poem says about love, if true, in part determines whether or not men have loved.”  Nelson quotes Ingram and Redpath who are in agreement with his statement when they paraphrase the couplet in an extended form: "If this is a judgment (or a heresy), and this can be proved against me, and by citing my own case in evidence, then I've never written anything, and no man's love has ever been real love."”  Vendler states “Therefore, if he himself is in error on the subject of what true love is, then no man has ever loved; certainly the young man (it is implied) has not loved, if he has not loved after the steady fashion urged by the speaker, without alteration, removals, or impediments”  Each of these authorities agree in the essence of the Sonnet and its portrayal of what love really is and what it can withstand, for example, the test of time and the fading of physical attraction of the object of our love. The couplet is, therefore, that men have indeed loved both in true and honest affection (this being the most important part of the argument) as well as falsely in the illusions of beauty before just as Shakespeare has written before this sonnet.