Sheridan wrote this drama in part to satirise the extent that sentimentalism held sway over certain members of the upper classes, particularly women. This was due to the rise of the novel at the time, and the novels that Lydia Languish sends her servingwoman to acquire for her in Act I scene 2 were real novels of the time that were characterised by sentimentality, or the dominance of feeling over any rational thought. Lydia, as her last name of "Languish" suggests, wishes to live her life as if it were a novel, and is shown to be so sentimental that she forces her lover, Captain Absolute, to pretend to be less than he is, a mere Ensign, in order to court her. Throughout the play, her sentimentality is ridiculed. A great example is when she is worried that she has not had a quarrel with her lover, and so writes herself a letter telling her that he has been paying his attentions elsewhere. Note how Julia is given the final words of the play, which argue for a more measured, anti-sentimental approach to romance and love:
...while hope pictures to us a flattering scene of future bliss, let us deny its pencil those colours which are too bright to be lasting. When hearts deserving happiness would unite their fortunes, virtue would crown them with an unfading garland of modest, hurtless flowers; but ill-judging passion will force the guadier rose into the wreath, whose thorn offends them, when its leaves are dropped!
The message is clear: practising the kind of "ill-judging passion" that Julia refers to will not bring lasting happiness. It is only through "modest, hurtless flowers" that this can be achieved. Sentimentality as it is exhibited by Lydia Languish is not only satirised and ridiculed, it is also shown to guarantee unhappiness, as you come to expect far more than can be reasonably delivered.