"It is true, as to civil and common conversation, the general names of substances, regulated in their ordinary signification by some obvious qualities... do well enough to design the things men would be understood to speak of... But in philosophical inquiries and debates, where general truths are to be established, and consequences drawn from positions laid down, there the precise signification of the names of substances will be found not only not to be well established, but also very hard to be so." (821-822)I feel the need to argue the ease at which Locke's two uses of the communication by words can be distinguished. "These two uses are very distinct; and a great deal less exactness will serve in the one than in the other, as we shall see in what follows." (817) He seems, merely by defining the two uses in a sentence, to assume the exact signification of his idea to be conveyed -- which seems contrary to his point. This is part of the foundation of his text. It is right at the beginning of Chapter IX. You would think he would spend a little more time discussing the significatory differences between these two terms.
I do not think these two uses can be so easily separated. Does not every discourse, no matter how common, contain aspects of what Locke defines the "philosophical" use? Does not every utterance have some goal to ascertain general truths and develop consequences? (822, quoted above) Even in a common exchange between close friends -- perhaps in which they are middle school-age girls participating in the gossiping ritual customary for their sect -- is there not a certain element of truth which is aimed to find? Perhaps this truth would be viewed as too common to be of importance to Locke -- such as if Suzy likes Billy now or if she still likes Luck -- but is nevertheless, a pursuit of truth. (At least, a truth as I understand the term. If Locke had unpacked and further defined his understanding of the philosophical use, maybe I would discover his usage of 'truth' has not the same signification as my 'truth.')
Locke's point 15 is preceded by the epitaph "With this imperfection, they may serve for civil, but not well for philosophical use." (821) This precedes the first quote of this post. Why does Locke view imperfections in discourse acceptable when used in a civil sense but not in the philosophical sense? I would argue that imperfections of words are imperfections of words, regardless of use. Perhaps particular contexts carry with them a certain signification -- in other words, signification is contextual -- but this transcends Locke's classification through use. Civil conversations are just as fraught with miscommunication as philosophical ones -- perhaps even more so. For example, in a facebook chat message or a text message your friend may employ an abbreviation or acronym with which you are not altogether familiar with the meaning. Although the acronym 'lol' is commonly used to signify 'laugh out loud' it does not necessarily imply the writer is literally laughing out loud. Furthermore, the same acronym can also signify 'lots of luck,' 'lots of love' and countless other words combinations and clearly a degree of miscommunication. (While lol is an acronym, not a word, it has gained an emergent signification which I would say has earned it the title of a word in its own right. After all, some people pronounce it phonetically, effectively using it as a word.) In many communities aimed at philosophical inquiry, the use of words is more conscious and misunderstanding is less common nowadays. For example, scientists work with a particular definition of the term 'hypothesis' which is not used in exactly the same connotation as a common use of the word.
Locke confines the majority of his semiotic theory to the philosophical use of words -- which makes sense, as he had philosophical matters on the brain and his life's work was of the philosophical nature -- but his theories and claims can be applied to the civil use of words as well. In the philosophical uses words in our era, terms signifying a complex mode are often established as a basis of the inquiry. This, in conjunction with the lack of this practice in our civil discourse, makes the miscommunication of words more prevalent in today's civil methods of communication than philosophical.