Step 1: Understanding the Concept:
'Kēndrādhipatya Dōṣa' is a specific rule in Parāśari astrology. It states that natural benefics (Jupiter, Venus, Mercury, and the waxing Moon) lose their innate ability to give good results if they rule the 1st, 4th, 7th, or 10th houses. Conversely, natural malefics lose their maleficence if they rule these houses.
Step 2: Detailed Explanation:
Analysis of Assertion (A):
Jupiter (Guru) and Venus (Śukra) are the two 'Pūrṇa Śubha' (full benefics). The texts explicitly state that the flaw of Kendradhipatya is most prominent for these two planets. Mercury (Budha) also suffers from this, but to a lesser degree. This is because the strength of beneficence in Guru and Shukra is so high that its 'neutralization' by Kendra lordship is more impactful on the horoscope. Therefore, Assertion (A) is true.
Analysis of Reason (R):
The logic behind this Dosha is that the Kēndras (1, 4, 7, 10) are houses of 'Action' and 'Worldly Endeavor'. Natural benefics are 'soft' and 'spiritual' in nature. When they take over the administration (lordship) of these active houses, their soft nature is compromised, and they become neutral or even problematic for the specific house results. This process of a planet becoming 'Dōṣa-yukta' due to strong Kendra lordship is the very definition and explanation of the Kendradhipatya Dosha.
Causal Link:
Why is the Dosha strong for Guru and Shukra (A)? Because, as per the rule, natural benefics lose their nature upon becoming Kendra lords (R). Thus, (R) directly explains the mechanism mentioned in (A). Specifically, the Laghupārāśarī states: "Śubhāḥ kēndrādhipatayō na śubhaphaladāḥ" (Benefics as Kendra lords do not give auspicious results).
Step 3: Final Answer:
Both statements are true, and (R) is the correct technical explanation for why the Dosha applies to Jupiter and Venus.