foil - one that by contrast underscores or enhances the distinctive characteristics of another.
The thing I love about Jack is that Jack acts as a foil for the Doctor in the literary sense. That while he stands on his own as a character (and a loveable roguish one at that) his juxtaposition with the Doctor allows us to get even more development for both the Doctor and the Doctor/Rose relationship. Jack exists to be what the Doctor isn't--which gives Rose and the viewer a better appreciation for who and what the Doctor is, and his methods. Jack also exists to bring the two of them closer that much faster, but also to underscore the roadblocks and pitfalls the two have to overcome before they can get closer. Also, he's there to show that there's so much more than physical attraction going on here. That while physical attracting is all well and good, there is more to relationships than attraction and infatuation. They've been saying that all along, every time Jackie or Mickey or some random person like Jabe questions the Doctor and Rose's relationship. But with Jack, they're showing rather than telling, which is definitely a step forward.
What I love about adding Biggles to the mix is that he doesn't invalidate the idea that the Doctor and Rose are attracted to one another. His involvement with them damn near confirms it--albeit in subtext rather than text, which I enjoy because sometimes a light touch is more valuable than anvils which drop from the sky. But it takes what could be a painfully awkward soap opera sort of thing and acts as a window through which they can see themselves. His presence gives them the impetus to act, when otherwise they would have been trapped by emotional inertia. Never either of them making a move because they were paralysed by fear of destroying the relationship they prize most.
Jack's irreverence, honest attraction to them both, amusement at their dancing around one another (if you'll pardon the joke), all could be excruciating--and who knows? Next week I may be banging my head quietly against a wall--instead I find charming as well as good solid storytelling. In the 2 eps thus far, rather than being the 3rd wheel inserted as roadblock to their relationship, as I think many fans feared, he has instead been exactly the catalyst the relationship has needed to jump from one level to the next. And that jump is organic and feels natural to me, rather than forced and awkward.
What I love from the story-telling sense as well is that Jack as the Doctor's foil is a nice parallel to Adam as Rose's foil. People may have been scratching their heads at Adam's brief tenure as a companion--but it made perfect sense to me that he was only onboard for the one adventure. As a character, he was there to be motivated by greed in The Long Game so that Rose could be motivated by love in Father's Day. And the audience would then understand that while they both fucked up, what makes it different is their motivations for fucking up, and how they dealt with it after. If we hadn't had Adam getting left at home for being selfish, then it wouldn't have worked as well for Rose not being sent home for being selfish.
So now we've got Jack, who openly admits he's all about the self-preservation. However, he doesn't leave the Doctor and Rose in the lurch when he could have, he expresses genuine remorse for his actions, and seems genuinely contrite. So he gets to stay. He earns his place on the TARDIS, as it were.
Adam wasn't sorry for what he did. He was sorry for getting caught. Which is just about the worst sin in the eyes of both the Doctor and the viewers. And if there was any evidence at all that he might learn from his mistake, I think he might have been kept on. But there wasn't. His insistence that he was sorry rang utterly false, and the Doctor knew that. Hence being booted.
Jack, on the other hand, owns his mistakes. He did act in ignorance--he had no idea the medical transport had nanogenes in it. And he defends that fact. But he doesn't let it excuse him from taking responsibility for his actions. And he does everything in his power to correct his mistake, instead of trying to pretend he hadn't really made a mistake because it wasn't his fault. Hell, the guy's ready and willing to die to make up for it, with grace and dignity. Any qualms I had about him, that pretty much wiped them out, for me.
As much as I dislike "Father's Day" for the cheap, blatant emotional manipulation, I do like that Rose doesn't get off easy. Her act wasn't premeditated as Adam's was. She wasn't in full possession of the facts when she impulsively tried to save her father's life to spare her mother and herself being miserable. It was her actions after that which the Doctor judged her harshly for, and she was genuinely sorry and definitely learned from her mistakes. The hard way, since it involved watching the Doctor die right in front of her. To be fair, the writers have pulled a bit of a Lana Lang and had most of her truly glorious fuck-ups be due to her lacking all the information, rather than making an informed decision that she knew was the wrong one. But I do like that Rose learned, or at least showed she is willing to learn.
I buy the "Just say you're sorry," absolution precisely because I do think there are times when the only true crime you can commit is not to learn from your mistakes.
And what I like is that the characters do grow and change. We see Mickey earn the Doctor's respect. We see Jackie grow up a bit. We see both the Doctor and Rose learn from their actions.
The storytelling isn't perfect, but the characters do evolve.