Some recluses and priests declare these
excessively speculative views:
"Everything Exists"; which is the one extreme (Sarvastavadin Eternalism...).
Other recluses
and priests declare a just as far fetched opposite extreme
view: "Everything does Not Exist" (Sunyatavadin Annihilationism...).
Avoiding both these extremes the Well-Gone-Beyond Buddha teaches
this Dhamma from the
subtle, exquisite, and profound middle:
When this is present,
that also exists.
When
this emerges,
that also arises.
When
this
is absent, that neither exists.
When
this ceases,
that also vanishes.
From ignorance arises mental
construction.
From mental construction arises consciousness.
From consciousness arises naming-&-forming.
From name-&-form arises the six senses.
From the six senses arises contact.
From contact arises feeling.
From feeling arises craving.
From craving arises clinging.
From clinging arises becoming.
From becoming arises birth.
From birth arises ageing, decay, sickness
and death.
From ageing, decay and death arises
Suffering..
This is the origin of this entire mass of
frustrating
Pain...
When ignorance ceases, mental construction stops.
When mental construction ceases, consciousness stops.
When consciousness ceases, naming-&-forming stops.
When name-&-form ceases, the six senses stops.
When the six senses ceases, contact stops.
When contact ceases, feeling stops.
When feeling ceases, craving stops.
When craving ceases, clinging stops.
When clinging ceases, becoming stops.
When becoming ceases, birth stops.
When birth ceases, ageing, decay,
and death stops... !
When ageing, decay and death ceases,
then Suffering stops!
This is the
disappearance of this entire mass of
frustrating
Pain...
This - only this supremely stilled silence - is
the deathless Nibbāna!

Everything has a Cause:
More on Co-Dependent
Co-Arising (paticca-samuppāda):
https://What-Buddha-Said.net/drops/IV/Caused_by_What.htm
https://What-Buddha-Said.net/drops/Cohesive_Co-Origination.htm
https://What-Buddha-Said.net/drops/Collapsible_Co-Cessation.htm
https://What-Buddha-Said.net/drops/III/Causes_of_Emergence.htm
https://What-Buddha-Said.net/library/DPPN/wtb/n_r/paticca_samuppaada.htm

Existence is dynamic thus:
Neither a static substance out there,
nor a mental illusion in here,
But a chain of dependent states arising and ceasing momentarily...
More on
Buddhist Ontology: What exists and how does it exist?
https://What-Buddha-Said.net/drops/What_Exists.htm
https://What-Buddha-Said.net/drops/Advanced_Right_View.htm