is buddhism just an offshoot of hinduism?

I've often heard it said that Buddhism is simply an offshoot of Hinduism, but is there any truth to that claim? I'd argue no. While they both come from the same region and share similar terminology, making them a part of a larger tradition of Indian thought and philosophy spanning thousands of years, their connection isn't as one-sided as many assume.

To begin with, from what I understand, Hinduism is a relatively modern term (coined by the British if memory serves me right) that's used to describe a diverse collection of Indian spiritual traditions, many of which arose after the Buddha's lifetime. Much of the Mahabharata, including the Bhagavad Gita, for example, was most likely composed after the Buddha's lifetime, as was the Ramayana and the majority of the Puranas. In fact, I think it's fair to say that Buddhism actually influenced much of what we call 'Hinduism' today.

For example, it should be noted that the concept of anatman in Sankara's version of Advaita Vedanta is similar to the Buddhist anatta, being derived from it. In one of his commentaries, Sankara writes, "Whenever we deny something unreal, we do so with reference to something real; the unreal snake, e.g. is negatived with reference to the real rope." Sankara essentially used the notion of anatman to deny the reality of the individual self (atman) in favour of Brahman. Many of Sankara's critics actually accused him of being a Buddhist in disguise.

The Buddha, who was born into the khattiya (warrior) caste, was one of the great wandering ascetics (Pali: samana, Skt: shramana) who taught in the later Vedic Period, and whose teachings were considered heterodox because they rejected the authority of the Vedas, the self (atman) of the early Upanishads, and the four main social classes (varna).

The most prominent 'orthodox' tradition in northern India at that time was Brahmanism, which, of course, relied heavily on the Vedas for their religious authority, and included some of the early Upanishads as well. It's clear from the Suttas that the Buddha was extremely familiar with them, but it's unclear as to precisely how he acquired this knowledge. Being from a prominent family, it's possible that he studied them, or it could be that he learned of them while wandering and debating with other religious teachers.

In any case, while many people think of the the Buddha as a reformer of Brahmanism, I think it's more correct to say that he replaced it with his own unique philosophy, often redefining many of the key philosophical terms and concepts of his contemporaries, giving them his own meaning and context. This is clearly documented with a variety of words such as brahmin and kamma.

The Buddha was also an expert at word play, especially puns (which don't always translate well into English), and many of these were in reference to passages from the Vedas and Upanishads. Much of this was apparently lost on later Buddhist commentators, but has since been rediscovered by modern scholarship and textual analysis. Nevertheless, the Buddha wasn't limited to just puns, and he added his own unique ideas to Indian thought, e.g., his introduction of khandha as a technical philosophical term (and possibly nibbana as well). Moreover, in The Place of Buddhism in Indian Thought, Ananda Guruge writes:

Lastly, the contributions to Indian thought made by the Buddha should be carefully borne in mind. It was no doubt the Buddha's admirable sense of humility, which led to his statement that he was not an original thinker. His theory of Dependent Causation or Origination was the most remarkable contribution to Indian thought. It is unique in the history of philosophy.

So, in the end, I think it's safe to say that both Buddhism and Hinduism are closely related and have a lot in common, but I definitely wouldn't go so far as to say that Buddhism is just an offshoot of Hinduism. I think doing so is not only inaccurate, but does a disservice to both in that it denies their individual achievements in the history and progression of Indian thought.