¡¶the+critique+of+pure+reason_´¿´âÀíÐÔÅúÅС·

ÏÂÔØ±¾Êé

Ìí¼ÓÊéÇ©

the+critique+of+pure+reason_´¿´âÀíÐÔÅúÅÐ- µÚ38²¿·Ö


°´¼üÅÌÉÏ·½Ïò¼ü ¡û »ò ¡ú ¿É¿ìËÙÉÏÏ·­Ò³£¬°´¼üÅÌÉ쵀 Enter ¼ü¿É»Øµ½±¾ÊéĿ¼ҳ£¬°´¼üÅÌÉÏ·½Ïò¼ü ¡ü ¿É»Øµ½±¾Ò³¶¥²¿£¡
£¨substance£©¡¡does¡¡not¡¡perish£»¡¡but¡¡that¡¡only¡¡the¡¡form¡¡of¡¡it¡¡undergoes
a¡¡change¡£¡¡In¡¡like¡¡manner¡¡was¡¡the¡¡saying£º¡¡¡¨From¡¡nothing¡¡es¡¡nothing£»¡¨
only¡¡another¡¡inference¡¡from¡¡the¡¡principle¡¡or¡¡permanence£»¡¡or¡¡rather
of¡¡the¡¡ever¡­abiding¡¡existence¡¡of¡¡the¡¡true¡¡subject¡¡in¡¡phenomena¡£¡¡For¡¡if
that¡¡in¡¡the¡¡phenomenon¡¡which¡¡we¡¡call¡¡substance¡¡is¡¡to¡¡be¡¡the¡¡proper
substratum¡¡of¡¡all¡¡determination¡¡of¡¡time£»¡¡it¡¡follows¡¡that¡¡all¡¡existence
in¡¡past¡¡as¡¡well¡¡as¡¡in¡¡future¡¡time£»¡¡must¡¡be¡¡determinable¡¡by¡¡means¡¡of¡¡it
alone¡£¡¡Hence¡¡we¡¡are¡¡entitled¡¡to¡¡apply¡¡the¡¡term¡¡substance¡¡to¡¡a
phenomenon£»¡¡only¡¡because¡¡we¡¡suppose¡¡its¡¡existence¡¡in¡¡all¡¡time£»¡¡a
notion¡¡which¡¡the¡¡word¡¡permanence¡¡does¡¡not¡¡fully¡¡express£»¡¡as¡¡it¡¡seems
rather¡¡to¡¡be¡¡referable¡¡to¡¡future¡¡time¡£¡¡However£»¡¡the¡¡internal¡¡necessity
perpetually¡¡to¡¡be£»¡¡is¡¡inseparably¡¡connected¡¡with¡¡the¡¡necessity
always¡¡to¡¡have¡¡been£»¡¡and¡¡so¡¡the¡¡expression¡¡may¡¡stand¡¡as¡¡it¡¡is¡£
¡¨Gigni¡¡de¡¡nihilo¡¡nihil£»¡¡in¡¡nihilum¡¡nil¡¡posse¡¡reverti£»¡¨*¡¡are¡¡two
propositions¡¡which¡¡the¡¡ancients¡¡never¡¡parted£»¡¡and¡¡which¡¡people
nowadays¡¡sometimes¡¡mistakenly¡¡disjoin£»¡¡because¡¡they¡¡imagine¡¡that¡¡the
propositions¡¡apply¡¡to¡¡objects¡¡as¡¡things¡¡in¡¡themselves£»¡¡and¡¡that¡¡the
former¡¡might¡¡be¡¡inimical¡¡to¡¡the¡¡dependence¡¡£¨even¡¡in¡¡respect¡¡of¡¡its
substance¡¡also£©¡¡of¡¡the¡¡world¡¡upon¡¡a¡¡supreme¡¡cause¡£¡¡But¡¡this
apprehension¡¡is¡¡entirely¡¡needless£»¡¡for¡¡the¡¡question¡¡in¡¡this¡¡case¡¡is
only¡¡of¡¡phenomena¡¡in¡¡the¡¡sphere¡¡of¡¡experience£»¡¡the¡¡unity¡¡of¡¡which
never¡¡could¡¡be¡¡possible£»¡¡if¡¡we¡¡admitted¡¡the¡¡possibility¡¡that¡¡new
things¡¡£¨in¡¡respect¡¡of¡¡their¡¡substance£©¡¡should¡¡arise¡£¡¡For¡¡in¡¡that¡¡case£»
we¡¡should¡¡lose¡¡altogether¡¡that¡¡which¡¡alone¡¡can¡¡represent¡¡the¡¡unity
of¡¡time£»¡¡to¡¡wit£»¡¡the¡¡identity¡¡of¡¡the¡¡substratum£»¡¡as¡¡that¡¡through¡¡which
alone¡¡all¡¡change¡¡possesses¡¡plete¡¡and¡¡thorough¡¡unity¡£¡¡This
permanence¡¡is£»¡¡however£»¡¡nothing¡¡but¡¡the¡¡manner¡¡in¡¡which¡¡we¡¡represent
to¡¡ourselves¡¡the¡¡existence¡¡of¡¡things¡¡in¡¡the¡¡phenomenal¡¡world¡£

¡¡¡¡*£§Persius£»¡¡Satirae£»¡¡iii¡£83¡­84¡£¡¡¡¨Nothing¡¡can¡¡be¡¡produced¡¡from
nothing£»¡¡nothing¡¡can¡¡be¡¡returned¡¡into¡¡nothing¡£¡¨£§

¡¡¡¡The¡¡determinations¡¡of¡¡a¡¡substance£»¡¡which¡¡are¡¡only¡¡particular¡¡modes
of¡¡its¡¡existence£»¡¡are¡¡called¡¡accidents¡£¡¡They¡¡are¡¡always¡¡real£»
because¡¡they¡¡concern¡¡the¡¡existence¡¡of¡¡substance¡¡£¨negations¡¡are¡¡only
determinations£»¡¡which¡¡express¡¡the¡¡non¡­existence¡¡of¡¡something¡¡in¡¡the
substance£©¡£¡¡Now£»¡¡if¡¡to¡¡this¡¡real¡¡in¡¡the¡¡substance¡¡we¡¡ascribe¡¡a
particular¡¡existence¡¡£¨for¡¡example£»¡¡to¡¡motion¡¡as¡¡an¡¡accident¡¡of
matter£©£»¡¡this¡¡existence¡¡is¡¡called¡¡inherence£»¡¡in¡¡contradistinction¡¡to
the¡¡existence¡¡of¡¡substance£»¡¡which¡¡we¡¡call¡¡subsistence¡£¡¡But¡¡hence¡¡arise
many¡¡misconceptions£»¡¡and¡¡it¡¡would¡¡be¡¡a¡¡more¡¡accurate¡¡and¡¡just¡¡mode
of¡¡expression¡¡to¡¡designate¡¡the¡¡accident¡¡only¡¡as¡¡the¡¡mode¡¡in¡¡which
the¡¡existence¡¡of¡¡a¡¡substance¡¡is¡¡positively¡¡determined¡£¡¡Meanwhile£»¡¡by
reason¡¡of¡¡the¡¡conditions¡¡of¡¡the¡¡logical¡¡exercise¡¡of¡¡our¡¡understanding£»
it¡¡is¡¡impossible¡¡to¡¡avoid¡¡separating£»¡¡as¡¡it¡¡were£»¡¡that¡¡which¡¡in¡¡the
existence¡¡of¡¡a¡¡substance¡¡is¡¡subject¡¡to¡¡change£»¡¡whilst¡¡the¡¡substance
remains£»¡¡and¡¡regarding¡¡it¡¡in¡¡relation¡¡to¡¡that¡¡which¡¡is¡¡properly
permanent¡¡and¡¡radical¡£¡¡On¡¡this¡¡account£»¡¡this¡¡category¡¡of¡¡substance
stands¡¡under¡¡the¡¡title¡¡of¡¡relation£»¡¡rather¡¡because¡¡it¡¡is¡¡the¡¡condition
thereof¡¡than¡¡because¡¡it¡¡contains¡¡in¡¡itself¡¡any¡¡relation¡£
¡¡¡¡Now£»¡¡upon¡¡this¡¡notion¡¡of¡¡permanence¡¡rests¡¡the¡¡proper¡¡notion¡¡of¡¡the
conception¡¡change¡£¡¡Origin¡¡and¡¡extinction¡¡are¡¡not¡¡changes¡¡of¡¡that¡¡which
originates¡¡or¡¡bees¡¡extinct¡£¡¡Change¡¡is¡¡but¡¡a¡¡mode¡¡of¡¡existence£»
which¡¡follows¡¡on¡¡another¡¡mode¡¡of¡¡existence¡¡of¡¡the¡¡same¡¡object£»¡¡hence
all¡¡that¡¡changes¡¡is¡¡permanent£»¡¡and¡¡only¡¡the¡¡condition¡¡thereof¡¡changes¡£
Now¡¡since¡¡this¡¡mutation¡¡affects¡¡only¡¡determinations£»¡¡which¡¡can¡¡have
a¡¡beginning¡¡or¡¡an¡¡end£»¡¡we¡¡may¡¡say£»¡¡employing¡¡an¡¡expression¡¡which¡¡seems
somewhat¡¡paradoxical£º¡¡¡¨Only¡¡the¡¡permanent¡¡£¨substance£©¡¡is¡¡subject¡¡to
change£»¡¡the¡¡mutable¡¡suffers¡¡no¡¡change£»¡¡but¡¡rather¡¡alternation£»¡¡that
is£»¡¡when¡¡certain¡¡determinations¡¡cease£»¡¡others¡¡begin¡£¡¨
¡¡¡¡Change£»¡¡when£»¡¡cannot¡¡be¡¡perceived¡¡by¡¡us¡¡except¡¡in¡¡substances£»¡¡and
origin¡¡or¡¡extinction¡¡in¡¡an¡¡absolute¡¡sense£»¡¡that¡¡does¡¡not¡¡concern
merely¡¡a¡¡determination¡¡of¡¡the¡¡permanent£»¡¡cannot¡¡be¡¡a¡¡possible
perception£»¡¡for¡¡it¡¡is¡¡this¡¡very¡¡notion¡¡of¡¡the¡¡permanent¡¡which
renders¡¡possible¡¡the¡¡representation¡¡of¡¡a¡¡transition¡¡from¡¡one¡¡state
into¡¡another£»¡¡and¡¡from¡¡non¡­being¡¡to¡¡being£»¡¡which£»¡¡consequently£»¡¡can¡¡be
empirically¡¡cognized¡¡only¡¡as¡¡alternating¡¡determinations¡¡of¡¡that
which¡¡is¡¡permanent¡£¡¡Grant¡¡that¡¡a¡¡thing¡¡absolutely¡¡begins¡¡to¡¡be£»¡¡we
must¡¡then¡¡have¡¡a¡¡point¡¡of¡¡time¡¡in¡¡which¡¡it¡¡was¡¡not¡£¡¡But¡¡how¡¡and¡¡by
what¡¡can¡¡we¡¡fix¡¡and¡¡determine¡¡this¡¡point¡¡of¡¡time£»¡¡unless¡¡by¡¡that¡¡which
already¡¡exists£¿¡¡For¡¡a¡¡void¡¡time¡­¡¡preceding¡­¡¡is¡¡not¡¡an¡¡object¡¡of
perception£»¡¡but¡¡if¡¡we¡¡connect¡¡this¡¡beginning¡¡with¡¡objects¡¡which
existed¡¡previously£»¡¡and¡¡which¡¡continue¡¡to¡¡exist¡¡till¡¡the¡¡object¡¡in
question¡¡in¡¡question¡¡begins¡¡to¡¡be£»¡¡then¡¡the¡¡latter¡¡can¡¡only¡¡be¡¡a
determination¡¡of¡¡the¡¡former¡¡as¡¡the¡¡permanent¡£¡¡The¡¡same¡¡holds¡¡good¡¡of
the¡¡notion¡¡of¡¡extinction£»¡¡for¡¡this¡¡presupposes¡¡the¡¡empirical
representation¡¡of¡¡a¡¡time£»¡¡in¡¡which¡¡a¡¡phenomenon¡¡no¡¡longer¡¡exists¡£
¡¡¡¡Substances¡¡£¨in¡¡the¡¡world¡¡of¡¡phenomena£©¡¡are¡¡the¡¡substratum¡¡of¡¡all
determinations¡¡of¡¡time¡£¡¡The¡¡beginning¡¡of¡¡some£»¡¡and¡¡the¡¡ceasing¡¡to¡¡be
of¡¡other¡¡substances£»¡¡would¡¡utterly¡¡do¡¡away¡¡with¡¡the¡¡only¡¡condition
of¡¡the¡¡empirical¡¡unity¡¡of¡¡time£»¡¡and¡¡in¡¡that¡¡case¡¡phenomena¡¡would
relate¡¡to¡¡two¡¡different¡¡times£»¡¡in¡¡which£»¡¡side¡¡by¡¡side£»¡¡existence¡¡would
pass£»¡¡which¡¡is¡¡absurd¡£¡¡For¡¡there¡¡is¡¡only¡¡one¡¡time¡¡in¡¡which¡¡all
different¡¡times¡¡must¡¡be¡¡placed£»¡¡not¡¡as¡¡coexistent£»¡¡but¡¡as¡¡successive¡£
¡¡¡¡Accordingly£»¡¡permanence¡¡is¡¡a¡¡necessary¡¡condition¡¡under¡¡which¡¡alone
phenomena£»¡¡as¡¡things¡¡or¡¡objects£»¡¡are¡¡determinable¡¡in¡¡a¡¡possible
experience¡£¡¡But¡¡as¡¡regards¡¡the¡¡empirical¡¡criterion¡¡of¡¡this¡¡necessary
permanence£»¡¡and¡¡with¡¡it¡¡of¡¡the¡¡substantiality¡¡of¡¡phenomena£»¡¡we¡¡shall
find¡¡sufficient¡¡opportunity¡¡to¡¡speak¡¡in¡¡the¡¡sequel¡£

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡B¡£¡¡SECOND¡¡ANALOGY¡£

¡¡¡¡¡¡¡¡¡¡¡¡Principle¡¡of¡¡the¡¡Succession¡¡of¡¡Time¡¡According
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡to¡¡the¡¡Law¡¡of¡¡Causality¡£

¡¡¡¡¡¡¡¡¡¡All¡¡changes¡¡take¡¡place¡¡according¡¡to¡¡the¡¡law¡¡of¡¡the
¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡connection¡¡of¡¡Cause¡¡and¡¡Effect¡£

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡PROOF¡£

¡¡¡¡£¨That¡¡all¡¡phenomena¡¡in¡¡the¡¡succession¡¡of¡¡time¡¡are¡¡only¡¡changes£»¡¡that
is£»¡¡a¡¡successive¡¡being¡¡and¡¡non¡­being¡¡of¡¡the¡¡determinations¡¡of
substance£»¡¡which¡¡is¡¡permanent£»¡¡consequently¡¡that¡¡a¡¡being¡¡of
substance¡¡itself¡¡which¡¡follows¡¡on¡¡the¡¡non¡­being¡¡thereof£»¡¡or¡¡a
non¡­being¡¡of¡¡substance¡¡which¡¡follows¡¡on¡¡the¡¡being¡¡thereof£»¡¡in¡¡other
words£»¡¡that¡¡the¡¡origin¡¡or¡¡extinction¡¡of¡¡substance¡¡itself£»¡¡is
impossible¡­¡¡all¡¡this¡¡has¡¡been¡¡fully¡¡established¡¡in¡¡treating¡¡of¡¡the
foregoing¡¡principle¡£¡¡This¡¡principle¡¡might¡¡have¡¡been¡¡expressed¡¡as
follows£º¡¡¡¨All¡¡alteration¡¡£¨succession£©¡¡of¡¡phenomena¡¡is¡¡merely
change¡¨£»¡¡for¡¡the¡¡changes¡¡of¡¡substance¡¡are¡¡not¡¡origin¡¡or¡¡extinction£»
because¡¡the¡¡conception¡¡of¡¡change¡¡presupposes¡¡the¡¡same¡¡subject¡¡as
existing¡¡with¡¡two¡¡opposite¡¡determinations£»¡¡and¡¡consequently¡¡as
permanent¡£¡¡After¡¡this¡¡premonition£»¡¡we¡¡shall¡¡proceed¡¡to¡¡the¡¡proof¡££©
¡¡¡¡I¡¡perceive¡¡that¡¡phenomena¡¡succeed¡¡one¡¡another£»¡¡that¡¡is¡¡to¡¡say£»¡¡a
state¡¡of¡¡things¡¡exists¡¡at¡¡one¡¡time£»¡¡the¡¡opposite¡¡of¡¡which¡¡existed¡¡in¡¡a
former¡¡state¡£¡¡In¡¡this¡¡case£»¡¡then£»¡¡I¡¡really¡¡connect¡¡together¡¡two
perceptions¡¡in¡¡time¡£¡¡Now¡¡connection¡¡is¡¡not¡¡an¡¡operation¡¡of¡¡mere
sense¡¡and¡¡intuition£»¡¡but¡¡is¡¡the¡¡product¡¡of¡¡a¡¡synthetical¡¡faculty¡¡of
imagination£»¡¡which¡¡determines¡¡the¡¡internal¡¡sense¡¡in¡¡respect¡¡of¡¡a
relation¡¡of¡¡time¡£¡¡But¡¡imagination¡¡can¡¡connect¡¡these¡¡two¡¡states¡¡in
two¡¡ways£»¡¡so¡¡that¡¡either¡¡the¡¡one¡¡or¡¡the¡¡other¡¡may¡¡antecede¡¡in¡¡time£»
for¡¡time¡¡in¡¡itself¡¡cannot¡¡be¡¡an¡¡object¡¡of¡¡perception£»¡¡and¡¡what¡¡in¡¡an
object¡¡precedes¡¡and¡¡what¡¡follows¡¡cannot¡¡be¡¡empirically¡¡determined¡¡in
relation¡¡to¡¡it¡£¡¡I¡¡am¡¡only¡¡conscious£»¡¡then£»¡¡that¡¡my¡¡imagination
places¡¡one¡¡state¡¡before¡¡and¡¡the¡¡other¡¡after£»¡¡not¡¡that¡¡the¡¡one¡¡state
antecedes¡¡the¡¡other¡¡in¡¡the¡¡object¡£¡¡In¡¡other¡¡words£»¡¡the¡¡objective
relation¡¡of¡¡the¡¡successive¡¡phenomena¡¡remains¡¡quite¡¡undetermined¡¡by
means¡¡of¡¡mere¡¡perception¡£¡¡Now¡¡in¡¡order¡¡that¡¡this¡¡relation¡¡may¡¡be
cognized¡¡as¡¡determined£»¡¡the¡¡relation¡¡between¡¡the¡¡two¡¡states¡¡must¡¡be¡¡so
cogitated¡¡that¡¡it¡¡is¡¡thereby¡¡determined¡¡as¡¡necessary£»¡¡which¡¡of¡¡them
must¡¡be¡¡placed¡¡before¡¡and¡¡which¡¡after£»¡¡and¡¡not¡¡conversely¡£¡¡But¡¡the
conception¡¡which¡¡carries¡¡with¡¡it¡¡a¡¡necessity¡¡of¡¡synthetical¡¡unity£»¡¡can
be¡¡none¡¡other¡¡than¡¡a¡¡pure¡¡conception¡¡of¡¡the¡¡understanding¡¡which¡¡does
not¡¡lie¡¡in¡¡mere¡¡perception£»¡¡and¡¡in¡¡this¡¡case¡¡it¡¡is¡¡the¡¡conception¡¡of
¡¨the¡¡relation¡¡of¡¡cause¡¡and¡¡effect£»¡¨¡¡the¡¡former¡¡of¡¡which¡¡determines¡¡the
latter¡¡in¡¡time£»¡¡as¡¡its¡¡necessary¡¡consequence£»¡¡and¡¡not¡¡as¡¡something
which¡¡might¡¡possibly¡¡antecede¡¡£¨or¡¡which¡¡might¡¡in¡¡some¡¡cases¡¡not¡¡be
perceived¡¡to¡¡follow£©¡£¡¡It¡¡follows¡¡that¡¡it¡¡is¡¡only¡¡because¡¡we¡¡subject
the¡¡sequence¡¡of¡¡phenomena£»¡¡and¡¡consequently¡¡all¡¡change£»¡¡to¡¡the¡¡law
of¡¡causality£»¡¡that¡¡experience¡¡itself£»¡¡that¡¡is£»¡¡empirical¡¡cognition
of¡¡phenomena£»¡¡bees¡¡possible£»¡¡and¡¡consequently£»¡¡that¡¡phenomena
themselves£»¡¡as¡¡objects¡¡of¡¡experience£»¡¡are¡¡possible¡¡only¡¡by¡¡virtue¡¡of
this¡¡law¡£
¡¡¡¡Our¡¡apprehension¡¡of¡¡the¡¡manifold¡¡of¡¡phenomena¡¡is¡¡always
successive¡£¡¡The¡¡representations¡¡of¡¡parts¡¡succeed¡¡one¡¡another¡£
Whether¡¡they¡¡succeed¡¡one¡¡another¡¡in¡¡the¡¡object¡¡also£»¡¡is¡¡a¡¡second¡¡point
for¡¡reflection£»¡¡which¡¡was¡¡not¡¡contained¡¡in¡¡the¡¡former¡£¡¡Now¡¡we¡¡may
certainly¡¡give¡¡the¡¡name¡¡of¡¡object¡¡to¡¡everything£»¡¡even¡¡to¡¡every
representation£»¡¡so¡¡far¡¡as¡¡we¡¡are¡¡conscious¡¡thereof£»¡¡but¡¡what¡¡this¡¡word
may¡¡mean¡¡in¡¡the¡¡case¡¡of¡¡phenomena£»¡¡not¡¡merely¡¡in¡¡so¡¡far¡¡as¡¡they¡¡£¨as
representations£©¡¡are¡¡objects£»¡¡but¡¡only¡¡in¡¡so¡¡far¡¡as¡¡they¡¡indicate¡¡an
object£»¡¡is¡¡a¡¡question¡¡requiring¡¡deeper¡¡consideration¡£¡¡In¡¡so¡¡far¡¡as
they£»¡¡regarded¡¡merely¡¡as¡¡representations£»¡¡are¡¡at¡¡the¡¡same¡¡time¡¡objects
of¡¡consciousness£»¡¡they¡¡are¡¡not¡¡to¡¡be¡¡distinguished¡¡from
apprehension£»¡¡that¡¡is£»¡¡reception¡¡into¡¡the¡¡synthesis¡¡of¡¡imagination£»
and¡¡we¡¡must¡¡therefore¡¡say£º¡¡¡¨The¡¡manifold¡¡of¡¡phenomena¡¡is¡¡always
produced¡¡successively¡¡in¡¡the¡¡mind¡£¡¨¡¡If¡¡phenomena¡¡were¡¡things¡¡in
themselves£»¡¡no¡¡man¡¡would¡¡be¡¡able¡¡to¡¡conjecture¡¡from¡¡the¡¡succession
of¡¡our¡¡representations¡¡how¡¡this¡¡manifold¡¡is¡¡connected¡¡in¡¡the¡¡object£»
for¡¡we¡¡have¡¡to¡¡do¡¡only¡¡with¡¡our¡¡representations¡£¡¡How¡¡things¡¡may¡¡be
in¡¡themselves£»¡¡without¡¡regard¡¡to¡¡the¡¡representations¡¡through¡¡which
they¡¡affect¡¡us£»¡¡is¡¡utterly¡¡beyond¡¡the¡¡sphere¡¡of¡¡our¡¡cognition¡£¡¡Now
although¡¡phenomena¡¡are¡¡not¡¡things¡¡in¡¡themselves£»¡¡and¡¡are
nevertheless¡¡the¡¡only¡¡thing
СÌáʾ£º°´ »Ø³µ [Enter] ¼ü ·µ»ØÊéÄ¿£¬°´ ¡û ¼ü ·µ»ØÉÏÒ»Ò³£¬ °´ ¡ú ¼ü ½øÈëÏÂÒ»Ò³¡£ ÔÞһϠÌí¼ÓÊéÇ©¼ÓÈëÊé¼Ü