Letters and their Significance

"It takes two to write a letter as much as it takes two to make a quarrel." ---Elizabeth Drew

"In a man's letters his soul lies naked." Letter from Samuel Johnson, dated 1777. 

"Letters are useful as a means of expressing the ideal self...In letters we can reform without practice, beg without humiliation, snip and shape embarrassing experiences to the measure of our own desire." Elizabeth Hardwick

Though these three quotes may seem to contradict one another, the letters found in Humphry Clinker seem to actually complicate the relationship between the three.  We, the reader, only get one side of the story, and Drew's view on the doubleness of the letters proves that our knowledge of each situation found in the plot is biased to the point of the letter-writer.  However, Johnson and Hardwick have two very different opinions of the letter:  the letter as a truthful journal and the letter as an edited text.  How do these combine in Humphry Clinker?