Are the Āraṇyaká-s and the Upaniṣád-s part of the Véda?

Question

Mántra–Brā́hmaṇayor Veda-nāma-dheyám.

"The name 'Véda' is given to the Mántra and the Brā́hmaṇa."

—Āpastamba-şrāuta-sūtrá 24.1.31

Ádhi-Dāivam áth' ā́dhy-ātmam

ádhi-yajñam íti trayám

Mántreṣu Brā́hmaṇe c' āivá

Şrutám íty ábhi dhīyate.

"The three-fold knowledge pertaining to the Gods, the soul, and the sacrifice, found in the Mántra-s and in the Brā́hmaṇa, is considered the Şrutá (Véda)."

—Şāṅkhāyana-gr̥hya-sūtrá 1.2.5

Are the Āraṇyaká-s and the Upaniṣád-s part of the Véda? If so, then why did Āpastamba not mention it in his şrāuta-sūtrá as part of the Véda? Why are Āraṇyaká-s and the Upaniṣád-s not found under the definition of Şrutá (Véda)?

References from the Véda (obviously not from the Āraṇyaká-s and the Upaniṣád-s) itself is preferred.

Answer 1

First, one has to understand what the terms "mantra" and "brAhmaNa" mean. brAhmaNa here does not mean the brAhmaNa-texts (as in shatapatha-brAhmaNa or taittirIya-brAhmaNa), but statements (which were already canonical by the time these definitions were made) which prescribe actions (vidhi) or praise/deplore actions, or are philosophical in nature.

तत्र धर्मब्रह्मप्रतिपादकमपौरुषेयं प्रमाणवाक्यं वेदः । स च मन्त्रब्राह्मणात्मकः । तत्र मन्त्रा अनुष्ठानकारकभूतद्रव्यदेवताप्रकाशकाः । तेऽपि त्रिविधा ऋग्यजुःसामभेदात् । ... ब्राह्मणम् अपि त्रिविधम्,
विधिरूपम्, अर्थवादरूपं, तद्-उभय-विलक्षण-रूपं च । ... विध्यर्थवादोभय-विलक्षणं तु वेदान्त-वाक्यम् ।

says prasthANa-bheda of madhusUdana-sarasvatI.

One must understand that vedic compilations (saMhitAs, brAhmaNa-s etc..) usually contain both these types of statements (unusual for them to have only mantra-s or only brAhmaNa-s - as in the case of shakala-saMhitA or ekAgni-kANDa..) . As, such, Apastamba's quote do not perclude AraNyaka-s from being considered part of the veda-s. Indeed, they are traditionally considered to be part of the veda-s, since they often share many traits with saMhitA and brAhmaNa compilations. (As a matter of fact, for example, bRhadAraNyakopanIShat is part of shatapata-brAhmaNa; and AraNyaka-s are in a sense considered part of brAhmaNa-s.)