The word buy is used when discussing the act of purchasing or acquiring something. It is a verb that can indicate either the physical action of picking something up in a store and paying for it, or finalizing a purchase in a virtual environment, such as online shopping.

The word by is often employed when discussing proximity or location, specifying how something is accomplished, or identifying who performed a particular action. Using by allows readers or listeners to understand the method or agent behind something in a clear and concise manner.

Though buy and by sound remarkably similar, their usage couldn't be more different. Buy is an action verb that's all about making purchases. By, in contrast, is a versatile word that's most often a preposition, but can also act as an adverb, or sometimes a noun. Getting these two straight helps convey clear meaning, whether you're discussing transactions or describing the method by which something is done.