Mandukya Upanishad, Class 61

In the five verses 24 to 28,
Gowdapadha Chariya is refuting Buddhist system of philosophy.  The four
systems are:

1. Sowthranthika madham:  This philosopher says that
   there is an external world different from the observer, the subject. 
   The external world is different from the observer and is real; this real
   distinct external world is proved by prathyaksha pramanam; therefore, this
   philosophy presented in a nutshell as bahya prathyaksha vadhinaha
2. Vaibashika madham:  Close to first one and they
   also say there is an external world; it exists separate from the observer;
   the external world is real; This distinct real external world is
   proved by inference or reasoning. bahyana anumana vadhinaha
3. Yogachara madham:  There is no independent real
   external world at all separate from the subject.  Just there is no
   real dream world, separate from the observer, individual.  This philosopher
   can be defined as Bahyartha abava vadhinaha.  External is only an
   appearance
4. Madhyamika madham:  This is similar to the third
   one; they also so there is no external at all; There is no subject
   observer also.  Sarvartha abava vadhinaha.  Soonya vadhinaha.

The first two systems are refuted by
the third system.  The first two systems claim there is a real external
world whereas the third system says there is no external world separate from
consciousness.  This is close to advaidam, in establishing mithyatvam of
the world, and therefore Gowdapadha chariya joined this system to refute the
first two system. The first two systems quote the experiences as proof for
the existence of an external world.  This was refuted in verses 26 to 29
by saying that experience does not prove reality.  The best example being
the dream.  In dream we have clear experiences with corresponding external
objects.  During the dream we are very sure of experiences and
corresponding objects, but when we wake up, we find out there is no external
objects at all separate from the dreamer.  Similarly, there is no external
world separate from the observer.  When we look at the pot, we see a pot
with weight etc.  But up on inquiry you find out there is no substance
called pot, the weight, attributes etc. belong to clay.  When you are
touching a pot, you really are touching clay.  Because of lack of inquiry
it appears as a substance.  Similarly, the whole world looks real. 
In the first stage, we dismiss the object and retain the word.  Once you
dismiss the object, the word should also be dismissed.  Because without an
object there is no validity for the word.  All the padham and padhartham
are resolved into the the ahdishtanam, the chaithanyam.  Similar to
akaram, ukaram, and makaram getting resolved in silence.

Then how will you explain the
erroneous perception.  If you are talking about error, there should be a
right perception.  If you want to talk about wrong perception, there
should be a correct perception.  If there is a correct perception, then
there must be an external object.  Without an external object, the concept
of error can’t be there at all.  There is no right perception at all
because there is no world for perception at all.

Verse 28

First, we will take the second
part.  Because of the reasons given in the previous three verses, the
external world is not at all born and therefore there is no such thing called
external world or an object of an external experience.  If it is unreal
world, why does it feel real?  Feeling is not a valid knowledge – you may
feel like a prime minister, but you are not.  In dream, you feel the dream
world is real, but it is not.

The first part of the sentence is
addressing yogachara.  Common features for both are that there is no
object separate from consciousness.  The difference is in arriving at the
nature of consciousness.  The yogachara philosopher says consciousness is
a fleeting, flickering, temporary, momentary entity.  Therefore, the
meaning of the word I, the subject is this temporary consciousness.  How
am I momentary entity?  I have been continually existing for my
life.  Yogachara will say that you are not one momentary consciousness but
many momentary consciousness.  Momentary consciousness are constantly
replaced by another momentary consciousness.  Because of the continuous
flow, it looks as though there is a permanent atma.  There is no permanent
atma, but only a flow of temporary series of atma.  He gives two examples:

1. Perennial river:  If you look at Ganges, there is
   no permanent Ganges because the river is in constant flow.  You feel
   that the Ganges you saw last year is same the Ganges this year.  The
   water of Ganges you touch this moment is not the same water for the next
   moment.  Ganges is only a flow of temporary flow of water.  Similarly,
   atma.  There is no permanent consciousness at all.
2. Flame:  You feel that there is a permanent flame,
   but on inquiry you will find that the same flame does not continually
   exists.  If the flame exists permanently, the oil will be there permanent,
   but oil is getting depleted.  The flame is constantly getting renewed
   by oil.  The flame of first moment and flame of the second moment are
   not the same; they are only similar.

Permanent river and flame are brama;
Yogachara bowdha says the permanent consciousness and chaithanyam are
brama.  Chaithanyam is born, gone, born, gone; there is a constant flow of
chaithanyam.  Gowdapadha refutes this philosophy in three words. 
Consciousness is not born at all, it is eternal; you can’t talk about temporary
consciousness.  Sankarachariya elaborately argues for this concept:

Sankarachariya asks the question, if
you are talking about the flow of fleeting consciousness and according to you
this is atma.  Consciousness number 1 appears and disappears; then
Consciousness 2 comes and disappears; then 3 comes and disappears and so
on.  Who is talking about this arrival and departure?  Is it the
first one or second one or third one?  Number 1 can never talk about the
arrival of number 2.   Because when number 1 is there number 2 is not
there.  Similarly, number 2 cannot talk about number 1 or number 3.  Therefore,
no single member can talk about the flow of chanika vigyanam, If somebody
has to talk about arrival and departure, there must be somebody other than the
flow who is there permanently.  So, the one who talks about, who is the
witness of, who is aware of arrival and departure must not arrive and
depart.  Yogchara committed the mistake of taking consciousness as the
thoughts of mind.  These arriving and departing thoughts are witnessed by
this nithya chaithanyam and this nithya chaithanyam does not come and go. 
Anithya vigyanam is the reality for yogachara.  Nithhya vigyanam is the
reality for us.  Thoughts arrive and depart, what is permanent is I the
witness principle.  They are seeing the footprints of flying birds in the
sky; they are seeing something that is not there; they are seeing the
origination of consciousness; this is a wrong perception.

The fourth madhyamika says that
there is nothing in creation (soonyavadha); this means you are not there which
means your philosophy is not there also.

Verse 29

For the sake of refutation, we
discussed all other systems.  From verse 29 to 46, Gowdapadha summarizes
the vedanta chidhantha; Consciousness alone is real and eternal; the world
obtained in jagradha avastha and swapna avastha are both mithya; I am not
matter but that eternal consciousness in which the mithya matter appears and
disappears.  Mithya includes body matter, mind matter and world
matter.  Consciousness does not produce a real world.  Other system
claim that eternal Brahman produce the external world.  that assume the
Brahman is subject to change.  To be a karanam or a cause it should be
subject to change – savikaram.  The truth is Brahman is changeless; therefore,
it is not a kranam at all and can’t produce any real creation.  that is
the very nature of Brahman.  Changelessness is the very nature of
Brahman.   This changeless nature of Brahman will ever be the
same.  World was not born; world is not born; world will not be born; What
was, what is and will be is all Brahman.  This nature of Brahman will
never change.  If you accept that a world is born out of Brahman, you will
never get out of samsara.  Acceptance of real world is invitation for
permanent bondage; therefore, you should not accept it if you want moksha.