We just returned from a ski holiday, where I had an incredible time enjoying the Rocky Mountains with my family. I am nursing a couple of overuse injuries, so I walked and hiked more than skied, but it doesn’t really matter what physical activity you’re engaging in when the snowy Rockies tower around you against the blue sky and the Colorado sun warms your back. My kids skied all day, every day, so I also had time to peacefully read, shop, nap, and eat some great local food. By the time I had to ferry them from the mountain at 3pm daily, I was relaxed and ready to enjoy them.

Which made it somewhat jolting when mid-vacation, as the two of us chilled in his room après ski, my fifteen-year-old son, George, inquired: “Mom, are you happy?”

Now, he didn’t mean at that moment. He wanted to know if I liked my life, if I regularly enjoyed myself, if, at forty-eight, things had so far turned out as I’d hoped.

I was taken aback and could only stammer, “Yes, of course. Why? Don’t I seem happy?”

“You often seem so serious,” he replied.

In the conversation that ensued, we talked about adulthood, and how the needle on the fun-responsible spectrum started trending toward the right the older one got, as life made its demands and responsibilities mounted. It was an opportunity for me to explain to him why finding meaningful work was critical to being a happy adult, and why finding loving relationships was equally so. I told him that I had both of these, and that even though I didn’t skip around the room most days, I felt deeply content with my life, not to mention exceedingly grateful.

Later that night, as I lay in bed waiting for the melatonin to kick in against my lingering jet lag, I had to ask myself: Were you being honest with him? With yourself? You do often feel overwhelmed by your responsibilities raising a large family, you don’t walk around always smiling and giggling like your kids. Is there a fundamental lack of happiness that only your child had noticed? Moreover, is it everyone—or just you?

As often happens in such moments, my thoughts drifted to Aristotle (4th c. BC). As a biologist, he observed that all living things are goal-directed, and as a philosopher, argued that the supreme goal of human beings—that for the sake of which everything else is sought, but which is not itself sought for any further reason—is Happiness. What is Happiness, though, he wondered?

Well, it can’t be the pursuit of mere pleasure, for that would be too animal-like, not elevated enough for a thinking being. It also can’t lie in the accumulation of honor or wealth. These are external goods, that rely on others and are too easily taken away: “Happiness depends on ourselves.”

The key to the happiness or well-being of anything lies in the perfection of its function. So, say that a knife could be happy; its happiness would lie in its being a phenomenal cutting instrument, thereby fulfilling its purpose, realizing its maximum potential as a knife. Since what makes human beings unique is their rationality, living a life of activity guided by reason is what brings out the best in us, and most fully actualizes and perfects our human nature.

What exactly does this look like for you and me? It does not dictate the same life and lifestyle for everyone, but rather the structure of the particular life we each choose to lead. It suggests that no matter what our individual talents, passions, relationships, or pursuits, we find the most overall fulfillment as human beings by pursuing them and making our decisions in a manner that expresses our rationality. On the day-to-day, this means using practical reason to guide our decisions and actions, not allowing ourselves to be moved along by life’s forces, but rather taking the reigns ourselves.

This isn’t to say that a fully human life is devoid of feeling. For Aristotle, making proper rational choices involves having the right sorts of feelings for the right sorts of things, where one’s feelings support ones decisions rather than contradict them. Say you are a successful businesswoman making philanthropic plans for the year. Being “happy” in this activity involves having generous feelings that undergird your decisions about how much to give, and when, and to whom. A person whose passions are at odds with what reason says must be deeply unhappy. (I discuss how he believes we develop proper feelings here.)

Can I tell George that, according to the “master of them that know,” I am, albeit often “serious,” nonetheless happy?

In light of the choices I’ve made and how they’ve made me feel about myself and my life, I think that I can—with the addition of Aristotle’s caveat that a thoroughly rational life still needs a few additional things to perfect it, including friends, adequate wealth, and, of course, good health. He didn’t mention sheer, mindless fun, but to George’s point, I think it deserves prominent mention in his list, and perhaps we as overworked, harried adults need to remind ourselves of this more often. I know that I do. Happy 2015!