Second...

Second, we have the capacity for using these sounds as "Signs of internal Conceptions," with which we communicate our thoughts to each other. Third, in order to avoid the inconvenience of trying to have unique names for everything, we have the ability to employ words as general terms applied commonly to many particular things.

[Essay III i 1-3] Lesser creatures lack the third requisite and superior beings somehow communicate (in ways we cannot imagine) without the first, Locke supposed, but human beings rely upon spoken language as a primary vehicle for communication. Like thought itself, language is designed to serve the practical needs of human life. Language The question, then, is how we achieve our communicative goals, and Locke proposed a deceptively simple theory: words signify ideas.

Since my own ideas are inaccessible to others, I employ the articulate sounds of human speech as extrinsic sensible objects by means…