Samuel Richardson in his preface to Pamela in 1740 wrote:

If to divert and entertain, and at the same time to instruct and improve the minds of the youth of both sexes:

If to inculcate religion and morality in so easy and agreeable a manner, as shall render them equally delightful and profitable:

If to set forth, in the most exemplary lights, the parental, the filial, and the social duties: ...

If to effect all these good ends, in so probable, so natural, so lively a manner, as shall engage the passions of every sensible reader, and attach their regard to the story: ...

If these be laudable or worthy recommendations, the Editor of the following letters, which have their foundation both in Truth and Nature, ventures to assert, that all these ends are obtained here together. 

(Richardson, Samuel: Pamela; or Virtue Rewarded, first published 1740. Penguin, London, 1985. Richardson's italics.)

Pamela, or Virtue Rewarded was a best-seller in the eighteenth century, even to the extent that Pamela motifs appeared on teacups and fans! It changed ideas about the nature of the prose narrative, being not about the noble people of the land but about a young servant woman whose resistance to her master's attempts at seduction leads to his reformation and final marriage with her. It was written as a series of letters from Pamela to her parents, and these letters were purportedly to serve as models for letter-writing. Such novels which are both entertaining and instructive and about ordinary people, came to be seen as belonging to a genre called the novel of sentiment.

To what extent can The Sum of Us also be regarded as belonging to this genre?

Certainly, ideas about what constitutes religion and morality have changed since the eighteenth century, but is The Sum of Us a film script with concerns about human values? Alissa Tanskaya describes the film The Sum of Us as an 'humanitarian work' in her Cinema Papers review, maintaining that it 'is about the meaning and importance of all sorts of families' and that it 'promotes tolerance and understanding of our differences' (Tanskaya, Alissa: The Sum of Us, Cinema Papers, August 1994). It would be difficult to disagree with this or to deny that the film has a clear moral content aimed at reaching as wide an audience as possible, through ordinary characters, gentle humour, witty dialogue and a delightful setting. Both the film and its script can be classed like Richardson's Pamela as a film of sentiment, not in any derogatory sense, but in the sense that it is instructive while being entertaining.

The script, as Tanskaya says about the film, is about true love, in all its varieties and also about that lack of love and companionship which we call loneliness.