"From the greater emphasis of singularity, energetic speakers and writers sometimes use 'I' as representative of mankind at large. Thus: 'The current impressions received through the senses are not voluntary in origin. What _I_ see in walking is seen because _I_ have an organ of vision.' The question of general moral obligation is forcibly stated by Paley in the individual form, 'Why am _I_ obliged to keep my word?' It is sometimes well to confine the attention of the hearer or reader to his own relation to the matter under consideration, more especially in difficult or non-popular argument or exposition. The speaker, by using 'I,' does the action himself, or makes himself the example, the hearer being expected to put himself in the same position."--Bain's "Composition Grammar."
PRONOUNS OF THE SECOND PERSON. "Anomalous usages have sprung up in connection with these pronouns. The plural form has almost wholly superseded the singular; a usage more than five centuries old.[24]
"The motive is courtesy. The singling out of one person for address is supposed to be a liberty or an excess of familiarity; and the effect is softened or diluted by the fiction of taking in others. If our address is uncomplimentary, the sting is lessened by the plural form; and if the reverse, the shock to modesty is not so great. This is a refinement that was unknown to the ancient languages. The orators of Greece delighted in the strong, pointed, personal appeal implied in the singular 'thou.' In modern German, 'thou' (_du_) is the address of familiarity and intimacy; while the ordinary pronoun is the curiously indirect 'they' (_Sie_). On solemn occasions, we may revert to 'thou.' Cato, in his meditative soliloquy on reading Plato's views on the immortality of the soul before killing himself, says: 'Plato, _thou_ reasonest well.' So in the Commandments, 'thou' addresses to each individual an unavoidable appeal: '_Thou_ shall not----.' But our ordinary means of making the personal appeal is, 'you, _sir_,' 'you, _madam_,' 'my _Lord_, you----,' etc.; we reserve 'thou' for the special case of addressing the Deity. The application of the motive of courtesy is here reversed; it would be irreverent to merge this vast personality in a promiscuous assemblage.