In response to the new novel "Tender Is the Night" written by Scott, Hemingway criticizes Scott for describing Dick and Nicole, the characters that are based on the actual people that both Scott and Hemingway knew, in an unpredictable way. That is, Dick and Nicole were based on Gerald and Sara, but what they did in the novel was not the kind of things that Gerald and Sara would have done in real life. Hemingway also blamed Scott for not being inventive. Hemingway is reprehensible in that he compromised the artistic integrity by making false judgment on Scott's work, that he arbitrarily demarcated the limits of invention and imposed those limits to Scott, and that he used the concept of truth in a self-contradictory way.
To start with, Hemingway was abrupt and officious enough to tell another artist what to do, possibly compromising the integrity of work by the artist. Hemingway boldly wrote to Scott that Scott cannot make Dick and Nicole, the fictional characters in the novel by Scott, do what they you not do. Of course, it is implied that they here were the real life people, Gerald and Sara. The truth here is that even one of the very definitions of novel is to be creative. If there was anything to impose on a writer who is writing a novel, that would be to tell him to be original instead of being hackneyed or banal. Fiction is not like biography, in which it is mandatory to keep everything as truthful as possible. Once a writer starts writing a novel, it is completely the writer's choice to write the work based on the actuality or based on a new circumstances and ideas that he or she had crafted. Therefore, it was over the line for Hemingway to blame Scott's way of writing just because it was different from what Hemingway deemed acceptable; it could greatly harm the integrity of Scott's work.
Additionally, Hemingway's criticism against Scott's work is futile in that his own idea or limits of invention that he wants to impose on Scott is self-contradictory. In the letter, Hemingway scolds Scott by saying that he ought to write, invent, out of what he knows. The truth here is that the very idea of being inventive is derived from the concept of "thinking outside of the box." Hemingway's telling Scott to be inventive and keep the people's antecedents straight is like giving someone A and B and telling that someone to make A, B, and C without even thinking about C. In this case, Scott would have to depict the fictional characters identical to the real life characters, which is quite uninventive per say, but be distinctively inventive simultaneously. Hemingway should have gone over the limits of definition of invention that he had created first so that he could avoid making a self-contradictory claim and forcing it on Scott.
Last but not least, as foreshadowed in the arguments made above, Hemingway is fixated on the idea of making the characters act just as if they were the real people that they were based on. In the middle of the letter, Hemingway encourages Scott to make it all up, so truly that later it will happen that way. For Hemingway's bold suggestions and claims to be even remotely plausible, there is one condition that needs to be met. That condition is that both Hemingway and Scott know about Gerald and Sara to a degree that Hemingway and Scott know what Gerald and Sara want just by looking at their faces. For example, let's assume that Gerald and Sara were invited to a pleasant outing by Hemingway and Scott. They all had good time and of course Gerald and Sara acted in the same way they had done whenever they met Hemingway or Scott. Does that mean that Hemingway and Scott know exactly what they were thinking, exactly what how they behave themselves when they are not with Hemingway or Scott, and what they do when they are by themselves with no one else around? Probably not. What Hemingway and Scott know about them could be only a fragment of superficial facades of them. Henceforth, it would be doubtable, if not ludicrous, for either of them to maintain that they know every bit of Gerald and Sara and that they can expect what Gerald and Sara will do with one hundred percent accuracy.
In conclusion, Hemingway's reaction to Scott's new novel is self-contradictory and myopic in that Hemingway degraded the integrity of Scott's work by telling him what to do, by falsely constructing his own limits of invention and imposing them on Scott and his work, and by simple-mindedly assuming that he knows he is omniscient and knows the inner-selves of Gerald and Sara. Hemingway needs to acknowledge that he should not be pontificate to another artist unless he has a concrete and undeniable reason to do so. He should be able to achieve that goal by respecting others, becoming more reasonable, and by being self-effacing.