Lesson Two

"So, if you're a Time Lord, you're from Gallifrey. But, just because you're from Gallifrey that doesn't mean you're a Time Lord."

"Right."

They walked side-by-side through a crowded market on a technology-challenged-but-not-completely-obsolete planet on the outer edge of the Mutter's Spiral. A short, stocky man with oily hair and a smudged apron shouted from behind his booth that he had Daruhvian Ostrich Eggs, while a woman wearing no less than five dresses over each other - all in rags - called out that she had the finest woven silver neckplates in all the galaxy.

Rose glanced at the necklaces as they walked by, but they looked more like bundles of barbed wire than anything she'd want to wear.

"What brought on the question?" he asked.

"I don't know. Thought association, I guess," she answered absently as she looked ahead of them. Further down, there was a shop with reams of multi-colored fabric on giant bolts and baskets of beads that twinkled in the sunlight.

"Thought association. Right. So, me saying I need to stop by and get a mercury filter led you to a question about Time Lords?"

Rose laughed, and shook her head. "No. When you said you needed the filter, I said I thought we had some. And you said that what you had was a mercury liquid filter, and not a mercury steam filter. All mercury filters filter mercury, but not all mercury filters filter steam mercury."

He arched one eyebrow, which made the other eye blink. "Right. Of course. It's obvious now."

Rose nudged him with her elbow. "I was thinking that it reminded me of when I took logic in school. You know… if she's in the house, then she can't see the moon. But, if she can't see the moon, that doesn't mean she's in the house."

"That's how they teach you conditional logic? No wonder humans are struggling to build a better mousetrap, forget rockets," he mumbled, looking annoyed at the whole concept.

"You're missing the path."

"Actually, I see the path quite clearly. If all Time Lords are Gallifreyan, and I am a Time Lord, then I am Gallifreyan. However, that does not necessarily answer the question if all Gallifreyans are Time Lords, it's one way conditional."

"Right, so all Time Lords are Gallifreyan."

He drew a breath in through his teeth, which she'd learned was his 'Yes, well, you'd think so, wouldn't you...' sound. "At least in theory."

Rose looked up at him, but he didn't look in her direction, continuing down the aisle between booths. "Oh! Here we are! Mercury-Filters-A-Palooza."

While he bartered with the tall, thin man — he had to clear at least seven feet easy — Rose wandered to the booths on either side of the aisle. Every few minutes, she felt the Doctor's gaze as he sought her out, and she'd look back at him with a smile. No, she hadn't wandered off. When he came to her, she was inspecting a small gold fob with pretty engravings around the edge.

"Look at this, Doctor. It changes color with the weather."

"Haven't seen one of these in years," he said, taking it from her hand and tossing it in the air. "Bezoolium, right? Course, never really found the need to predict the weather. If I land and it's raining, I don't get out of the TARDIS." He grinned and put it back in her hand.

"Mum would love this. She's always complainin' 'bout the weatherman. This would be bang on every time. No more complaining."

His eyebrows shot up. "No more complaining from Jackie Tyler. We'll take it!"

With their purchases in one hand, and Rose's hand held in the other, they headed back through the market. The TARDIS was parked in a quiet alley several streets over, but the walk was pleasant. A soft breeze blew through the low buildings of the city, carrying the occassional whiff of something cooking. Rose watched him out of the corner of her eye.

"I can practically hear the cogs churning," he said, squeezing her fingers. "What are you thinking about?"

"Does it bother you that I ask?"

He didn't answer right away, and Rose held her breath. The last thing she wanted to do was hurt him, but she wanted to know about him... understand him. And he didn't volunteer anything that she didn't prod out of him first. So, she had to ask. Finally, he shook his head.

"No." He finally did look at her, and while there was a smile on his lips, his eyes didn't quite convince her. "It doesn't bother me. Sometimes, I don't like to answer. But, I always will."