Common Answers
Some of the more simplistic answers to this question include: Anyone born in
India is automatically a Hindu (the ethnicity fallacy), if your parents are
Hindu, then you are Hindu (the familial argument), if you are born into a certain
caste, then you are Hindu (the genetic inheritance model), if you believe in
reincarnation, then you are Hindu (forgetting that many non-Hindu religions
share at least some of the beliefs of Hinduism), if you practice any religion
originating from India, then you are a Hindu (the national origin fallacy).
The Real Answer
The real answer to this question has already been conclusively answered by the
ancient sages of Hinduism, and is actually much simpler to ascertain than we
would guess. The two primary factors that distinguish the individual uniqueness
of the great world religious traditions are a) the scriptural authority upon
which the tradition is based, and b) the fundamental religious tenet(s) that
it espouses. If we ask the question what is a Jew?, for example, the answer
is: someone who accepts the Torah as their scriptural guide and believes in
the monotheistic concept of God espoused in these scriptures. What is a Christian? -
a person who accepts the Gospels as their scriptural guide and believes that
Jesus is the incarnate God who died for their sins. What is a Muslim? - someone
who accepts the Qur'an as their scriptural guide, and believes that there is
no God but Allah, and that Mohammed is his prophet.
Scriptural Authority
In general, what determines whether a person is a follower of any particular
religion is whether or not they accept, and attempt to live by, the scriptural
authority of that religion. This is no less true of Hinduism than it is of any
other religion on earth. Thus, the question of what is a Hindu is similarly
very easily answered.
The Definition
By definition, a Hindu is an individual who accepts as authoritative the religious
guidance of the Vedic scriptures, and who strives to live in accordance with
Dharma, God's divine laws as revealed in the Vedic scriptures.
Only If You Accept the Vedas
In keeping with this standard definition, all of the Hindu thinkers of the six
traditional schools of Hindu philosophy (Shad-darshanas) insisted on the acceptance
of the scriptural authority of the Vedas (shabda-pramana) as the primary criterion
for distinguishing a Hindu from a non-Hindu, as well as distinguishing overtly
Hindu philosophical positions from non-Hindu ones. It has been the historically
accepted standard that, if you accept the Vedas (and by extension Bhagavad Gita,
Puranas, etc.) as your scriptural authority, and lived your life in accordance
with the Dharmic principles of the Vedas, you are then a Hindu. Thus, an Indian
who rejects the Veda is obviously not a Hindu. While an American, Russian, Indonesian
or Indian who does accept the Veda obviously is a Hindu.

