Such in a word is the theosophic relations between the three periods represented by the first Vedic Collection, the ritualistic Br[=a]hmanas, and the philosophical treatises called Upanishads.  Yet if one took these three strata of thought to be quite independent of each other he would go amiss.  Rather is it true that the Br[=a]hmanas logically continue what the hymns begin; that the Upanishads logically carry on the thought of the Br[=a]hmanas.  And more, for in the oldest Upanishads are traits that connect this class of writings (if they were written) directly, and even closely with the Vedic hymns themselves; so that one may safely assume that the time of the first Upanishads is not much posterior to that of the latest additions made to the Vedic collections, though this indicates only that these additions were composed at a much later period than is generally supposed.[2] In India no literary period subsides with the rise of its eventually ‘succeeding’ period.  All the works overlap.  Parts of the Br[=a]hmanas succeed, sometimes with the addition of whole books, their proper literary successors, the Upanishads.  Vedic hymns are composed in the Brahmanic period.[3] The prose S[=u]tras, which, in general, are earlier, sometimes post-date metrical C[=a]stra-rules.  Thus it is highly probable that, whereas the Upanishads began before the time of Buddha, the Catapatha Br[=a]hmana (if not others of this class) continued to within two or three centuries of our era; that the legal S[=u]tras were, therefore, contemporary with part of the Br[=a]hmanic period;[4] and that, in short, the end of the Vedic period is so knit with the beginning of the Br[=a]hmanic, while the Br[=a]hmanic period is so knit with the rise of the Upanishads, S[=u]tras, epics, and Buddhism, that one cannot say of any one:  ’this is later,’ ‘this is earlier’; but each must be taken only for a phase of indefinitely dated thought, exhibited on certain lines.  It must also be remembered that by the same class of works a wide geographical area may be represented; by the Br[=a]hmanas, west and east; by the S[=u]tras, north and south; by the Vedic poems, northwest and east to Benares (AV.); by the epics, all India, centred about the holy middle land near Delhi.

The meaning of Upanishad as used in the compositions themselves, is either, as it is used to-day, the title of a philosophical work; that of knowledge derived from esoteric teaching; or the esoteric teaching itself.  Thus brahma upanishad is the secret doctrine of brahma, and ‘whoever follows this upanishad’ means whoever follows this doctrine.  This seems, however, to be a meaning derived from the nature of the Upanishads themselves, and we are almost inclined to think that the true significance of the word was originally that in which alone occurs, in the early period, the combination upa-ni-[s.]ad, and this is purely external:  “he makes the common people upa-ni-s[=a]din,” i.e., ‘sitting below’ or ‘subject,’