In Jain philosophy this question is very important and comes exactly in the context of Bhagavatī Sūtra–style logical discussion:

“In one dravya (substance) how can there be both astitva (existence) and nāstitva (non‑existence)?”

Answer in simple steps:

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1. What is meant by astitva and nāstitva here?

• Astitva = “existence” of something
• Nāstitva = “non‑existence” of something

But Jain āchāryas do not mean:

• “the dravya itself exists and also does not exist” (that would be a contradiction).

They mean:

> In one and the same dravya, > – something about it exists, and > – something about it does not exist, > at the same time, but from different viewpoints (naya).

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2. Dravya vs Paryāya – key to the answer

Every reality has two aspects:

1. Dravya – the permanent substance (e.g. soul, matter, dharma, etc.)
2. Paryāya – its changing modes or states (e.g. “happy”, “sad”, “hot”, “cold”).

So:

• As dravya, it is eternal – it always exists.
• As a particular paryāya, it arises and vanishes – so each mode is non‑eternal.

Thus in one soul:

• The soul‑substance is always there → astitva.
• The present state (anger, knowledge‑level, body‑state, etc.) keeps changing → old mode’s nāstitva, new mode’s astitva.

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3. How both are together in one substance

Take a simple example:

• A person was ignorant in childhood and becomes more knowledgeable now.

For the same jīva (soul):

• The old ignorant state now has nāstitva (it has “ceased”).
• The new knowledgeable state now has astitva (it has “appeared”).
• Yet the soul‑dravya that went through these states remains the same and has continuous astitva.

So:

• Dravya‑level: existence (astitva) is never broken.
• Paryāya‑level: some modes are “no more” (nāstitva), some are present (astitva), some are yet to come.

Hence the statement: In the same dravya there is both astitva (of the dravya and current modes) and nāstitva (of past/future modes).

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4. Role of Anekāntavāda (non‑one‑sidedness)

Bhagavatī Sūtra questions are usually to bring out anekānta:

• From nischaya naya (real, substance‑view):

The soul (as dravya) always exists → only astitva.

• From vyavahāra naya (practical, mode‑view):

This particular state was, now is not → its nāstitva now.

So the same reality is:

• Sat (existent) in one respect,
• Asat (non‑existent) in another respect,

without any real contradiction.

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5. Digambar–Śvetāmbara note

On this point:

• Both traditions accept:

- Six dravyas, - The dravya–paryāya doctrine, - Anekāntavāda and the use of naya (standpoints).

• So the essence of the answer is the same in both:

One substance has eternal existence as dravya, and changing existence–non‑existence in its modes.

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Very short summary:

In one dravya, astitva is of the dravya (it never ceases), and nāstitva is of particular paryāyas (each mode arises and perishes). Seen with anekānta and naya, both “existence” and “non‑existence” correctly apply to the same substance in different respects, which is exactly what the Bhagavatī Sūtra discussion wants to teach.