"the branch of knowledge that deals with the structure, historical development, and relationships of a language or languages" (Google).
"Philology was an older term for linguistics, and especially for the branch of linguistic study devoted to comparative and historical research into the development of languages. In a wider sense, the term sometimes also covers the study of literary texts (https://answers.yahoo.com/question/index?qid=20100118032748AAvpahf accessed 8/1/14).
Definition from Wikipedia: Philology is the study of language in written historical sources; it is a combination of literary criticism, history, and linguistics. It is more commonly defined as the study of literary texts and written records, the establishment of their authenticity and their original form, and the determination of their meaning.
Classical philology is the philology of Classical Sanskrit, Greek and Classical Latin. Classical philology is historically primary, originating in Pergamum and Alexandria around the 4th century BCE, continued by Greeks and Romans throughout the Roman and Byzantine Empires, and eventually taken up by European scholars of the Renaissance, where it was soon joined by philologies of other languages both European (Germanic, Celtic, Slavistics, etc.) and non-European (Sanskrit, Persian, Arabic, Chinese, etc.). Indo-European studies involves the comparative philology of all Indo-European languages.
Etymology from Wikipedia: The term philology is derived from the Greek φιλολογια (philologia), from the terms φιλοσ (philos), meaning "love, affection, loved, beloved, dear, friend" and λογοσ (logos), meaning "word, articulation, reason", describing a love of learning, of literature as well as of argument and reasoning, reflecting the range of activities included under the notion of λογοσ. The term changed little with the Latin philologia, and later entered the English language in the 16th century, from the Middle French philologie, in the sense of "love of literature".
The adjective φιλολογοσ (philologos) meant "fond of discussion or argument, talkative", in Hellenistic Greek also implying an excessive ("sophistic") preference of argument over the love of true wisdom, φιλοσοφοσ (philosophos).
Comparative linguistics from Wikipedia (originally comparative philology) is a branch of historical linguistics that is concerned with comparing languages to establish their historical relatedness.
Genetic relatedness implies a common origin or proto-language, and comparative linguistics aims to construct language families, to reconstruct proto-languages and specify the changes that have resulted in the documented languages.
"The meaning of "love of learning and literature" was narrowed to "the study of the historical development of languages" (historical linguistics) in 19th century usage of the term due to the rapid progresses made in understanding sound laws and language change, the "golden age of philology", taken to last throughout the 19th century" (https://answers.yahoo.com/question/index?qid=20100118032748AAvpahf accessed 8/1/14).
"So, what is the difference between philology and linguistics (and, how can a philologist/linguist be--or be considered to be--a historian)? The difficulty in defining the difference is that the two fields partly overlap. Philology is essentially the study of texts, for whatever purpose the investigator has in mind. There are certain techniques, more or less scientific (i.e., involving measuring and counting), such as paleography and critical edition, that are largely used only by well-trained philologists--and thus, not by linguists. Also, the texts are nearly always pre-modern (the author[s]--and often the languages--are generally dead), and the investigation can, and often does, use practically any disciplinary approach known to modern academia--from anthropology to zoology--in order to elucidate the texts and languages of the texts. Conclusions drawn from this empirical study are often used by philologists in "comparative philology" or "historical-comparative philology," a sub-branch of the field which is, essentially, pure linguistics (I'm coming to that). I.e., these specialists are interested in the reconstruction of earlier stages of the languages they work with, and use strictly linguistic methodology--"Basic Linguistic Theory," as I think it's called by R.M.W. Dixon in his recent book The Rise and Fall of Languages, incidentally an impressive, thoughtful book that covers both "linguistics" and "comparative-historical philology". However, many philologists work primarily in literature, or history, or--most frequently--in a foreign language department, i.e., some other viable academic field where they can find work, because philology today has retreated so far under the pressure of linguistics that it is no longer represented as an academic unit per se in American universities (at least not to my knowledge). It is, instead, taught in language departments...
"Now, for linguistics. The discipline of linguistics is a modern development, as someone in the discussion has already noted. Although even Saussure was a historical philologist, the split between linguistics and philology would seem to have begun around his time. (Perhaps a historian of linguistics can clarify this point.) Although the Neogrammarians--the Indo-European historical philologists who developed the first "linguistic" theory--were essentially simply historical linguists, the idea of linguistics as something different from philology TODAY is based on the idea that "linguists" have theoretical and methodological training in the "scientific study" of language, both "Language" in general and languages, especially modern spoken languages. The focus on theoretical rigor--an idea actually established by the Neogrammarians, though most linguists today are unaware of the fact--is primarily what, to linguists, distinguishes them from philologists. While this is certainly untrue today, when historical philologists are simply the same as historical linguists--both use essentially the same methodology and theoretical framework, regardless of quibbles-- it is notable that linguistics has developed many subfields devoted to questions largely ignored by the earlier (not modern) historical-comparative philologists, such as syntax, typology, pragmatics, semantics, and so forth" (Chris Beckwith at https://linguistlist.org/issues/9/9-741.html LINGUIST List 9.741, posted 5/17/98).
Turner, James. Philology: The Forgotten Origins of the Modern Humanities. Princeton University Press, 2014.
Aristophanes Of Byzantium Aristophanes was the producer of a text of Homer and also edited Hesiod’s Theogony, Alcaeus, Pindar, Euripides, Aristophanes, and perhaps Anacreon. Many of the Arguments prefixed in the manuscripts to Greek tragedies and comedies are ascribed to Aristophanes... He revised and continued the Pinakes of Callimachus, a biographical history of Greek literature... In editing the work of lyric and dramatic poets he introduced innovations in metrical analysis and textual criticism that were widely adopted by later scholars.
Philology and the Humanities an excellent article by C.S. Mackay... "Modern Classical philolgy begins in the early Renaissance with Petrarch (1304-74). Petrarch was very unhappy with his contemporary world, and saw in the world of Roman antiquity as it was known to him through the texts of surviving Latin authors an image of a superior civilization. (Famously he said in his autobiographical sketch incubui unice inter multa ad notitiam vetustatis quoniam mihi semper aetas ista displicuit [I uniquely strove in the midst of many activities toward a knowledge of antiquity, since this age always displeased me]). This was an effort to improve the Christian world through the examination of the moral precepts of the ancients. Specifically he referred once to his interests as studia humanitatis, studies of humanity. Humanitas is literally "humanness" and is the word used by the Romans to describe civilized, cultured life: civilization is what distinguishes mankind from the beasts, and so that civilized life that which describes mankind in a normative sense. Petrarch used this expression once, but it was quickly picked up by those who carried on his interests, the humanists of the Renaissance... two very characteristic traits of Classical philology: the careful examination of the usage of individual words and the writing of line-by-line commentaries on ancient works, often concentrating on the explanation of words through the citation of parallels (examples of other usages adduced to illuminate the sense in the passage under discussion)."
Philology Ancient History Encyclopedia: "Philology is derived from the Greek terms φιλοσ (love) and λογοσ (word, reason) and literally means a love of words. It is the study of language in literary sources and is a combination of literary studies, history and linguistics. Philology is generally associated with Greek and Classical Latin, in which it is termed philologia. The study of philology originated in European Renaissance Humanism in regards to Classical Philology but this has since been combined to include in its definition the study of both European and non-European languages."
Colby Glass, MLIS