Pure, fresh ingredients are a sine qua non in good potions. Severus knew this, knew where to find the purest, freshest ingredients possible.

Harry knew this too, which is why he often found himself in some odd locality, helping Severus gather potions ingredients.

Harry didn't mind too much. After all, he knew quite a bit about relationships, even if he was awful at potions. Harry knew that love wasn't the only sine qua non in a successful marriage. Helping Severus was more important than anything else he could come up with.

After all, Severus was always very grateful.

And he was excellent company. Witty and sarcastic and simply astoundingly knowledgeable on everything. No matter where they went, Severus could educate him on the locals, the customs, the weather, the landscape…

And he always made excellent potions later.

Severus stirred the potion and looked up to see Harry enter. "How are you?" he asked pleasantly.

"Quite well, thank you. The potion working out?"

Severus nodded. "Of course. Excellent ingredients, excellent potions master… why wouldn't it?"

Harry frowned at him playfully. "You know just as well as I do that sometimes, no matter how well everything seems to fit together, there's one little thing that ruins everything."

"Are we still talking about potions?"

"Of course. What else would I be talking about?"

Severus shrugged. "You could've been talking about relationships, too. Harry? Are you happy?"

"Severus, I adore you."

"I adore you, too, but you now as well as I do that love isn't the only thing necessary in a good relationship. Are you trying to say something?"

"No! Severus, please. I was really only talking about potions. I love you. Love… it's not even strong enough word for how I feel for you."

Severus' face softened. "Okay. I was worried that you were trying to hide something in innocuous sentences about potions."

"Sev…" Harry said warningly. "You've gotta drop this subject."

Severus smiled. "Fine, fine. You want to lend me a hand?"

"Sure. But I'll need to go boggart-hunting soon. I'm doing the boggart lesson again, and the one I've used for the past four years exploded. Wanna help with that?"

"Of course," Severus answered. "Oh, I got something for you."

"What?"

"You never did ask what this potion is for."

Harry shrugged apologetically. "I figured you'd tell me if you wanted to. So, what is it?"

"It's an eyesight correction potion, if you're interested."

"Aren't you supposed to ask that before you start making the potion?"

"Well, yes. Especially since it's a specialized potion. You do recall what a specialized potion is?"

"I wasn't that bad in Potions. A potion made specifically to a person."

"Exactly."

"Yes, I'd like to not wear glasses. Thank you so much." Harry looked positively elated. He kissed Severus chastely. "You have the best surprises."

Severus smiled again. He knew, too, that love wasn't the only sine qua non in a marriage. Although, it helped quite a bit with all the other sine qua nons.

Sine qua non – noun. An essential condition or element; an indispensable thing. Word of the Day, February 18, 2008)