在英文中，快乐是一种能力可以用 "happiness" 表示。

快乐的来源可以是内在的，也可以是外在的。内在的快乐通常是指一种内心的平静、安宁和愉悦感，这种快乐常常是由人的心态、态度、价值观和信仰等内在因素带来的。外在的快乐则是由外界的事物、情况或活动带来的，比如获得成功、收获成果、结交好友等。

下面是一些有关快乐的英文例句：

"Happiness is a choice, not a result. Nothing will make you happy until you choose to be happy." (快乐是一种选择，而不是结果。除非你选择快乐，否则什么也不会让你快乐。)

"Happiness is not something ready made. It comes from your own actions." (快乐不是一件现成的东西。它来自你自己的行动。)

"Happiness is not the absence of problems, it's the abipty to deal with them." (快乐不是没有问题，而是有能力处理问题。)

"Happiness is the consequence of personal effort. You fight for it, strive for it, insist upon it, and sometimes even travel around the world looking for it." (快乐是个人努力的结果。你为它而战、为它而奋斗、坚持它，有时甚至会周游世界寻找它。)

"Happiness is the natural flow of pfe when you are apgned with your true self." (当你与真正的自我保持一致时，快乐就是生命的自然流动。)