'Veda' is said to be the Ultimate, the 'Truth". It is the 'shruti vakya', heard by the jnyani in a transcendental state (during their intense meditation on Brahman), a state of savikalpa samadhi! The adepts who sat in tapas for long periods like nine months (navaghvas) or ten months (dashaghvas) heard voices from space (akashavani). These ancient Rishis have instructed this knowledge to their trusted disciples who are pure and selfless. Thus we have shruti vakyas that need no other proof!
It is also stated that the Vedic doctrines enunciated in the Vedic literature do not belong to a particular Rishi of a particular time! May be, it is collected and codified later. The Veda was Ekayana of a lakh verses in the beginning and it goes to the credit of the learned sage Krishna Dvaipayana, who came to be known as Vyasa Deva, for classifying the voluminous literature into four functional divisions. The Rk Veda Samhita is the first division consisting of basic principles, the Rks (mantra). The Yajus are the mantra used for fire worship. the Saman are the mantra to praise the Gods. And, the Atharva Veda consist of mantra for use in daily life- for cure of ailments, social welfare, etc. It is interesting to note here how the mantra imparted by Brahma to his first-born of Mind or Will, Desire to become many, or iccha 'EkO'ham, bahusyam.
We have almost 24 Divisions and Sub-divisions that included Upanishads (Vedanta) of these Vedic Doctrines under the Category of Veda, Vedanga, Veda Upanga, Veda pratishakya, as well as, Veda under Brahmana (Mantra) and Aranyaka. The Aranyaka are mantra used by the adepts who retired to forests and practiced the Veda. The brahmanas are practiced by house-holders. A number of great Sages are associated with these divisions and it goes to the credit of a Minister under the King Krishna Deva Raya of Vijayanagara Empire, Sayana, who gave us a set of these codified literary works. Many old records are either lost (due to foods, fires, etc.) or, just not yet available since these are with some renown Pundits in remote villages! There are no concerted efforts by our youngsters to retrieve them and study, albeit much effort is made to preserve them in electronic devices.
It goes to the credit of Sri Maharshi Mahesh Yogi who has given us an entire set of these Vedic Literature, numbering almost 40 and, attributed these to our own Consciousness.
The Chart giving divisions and sub-divisions of Vedic Literature is given separately.