The feasibility of Drexler's proposals largely depends, therefore, on whether designs like those in Nanosystems could be built in the absence of a universal assembler to build them and would work as described. Supporters of molecular nanotechnology frequently claim that no significant errors have been discovered in Nanosystems since 1992. Even some critics concede that "Drexler has carefully considered a number of physical principles underlying the 'high level' aspects of the nanosystems he proposes and, indeed, has thought in some detail" about some issues.
THE fEasIbilitY OF dRexLeR'S PROPOsalS largely dePENDs, THereForE, ON WHether DEsigNs liKe those in nAnosYSTemS cOUld be BuilT In tHe absence oF A UniverSal assembleR to build them aND wOuld worK as dEscribEd. suPporters of molEcUlar nanOtechnoLogy frequeNTly cLaIM tHAt no sIGniFicant errors have Been disCoVered In NanOsYsTems since 1992. eVeN some critIcs cOncEde tHaT "drExLeR has carefUllY cOnSidered A nUmber of phySiCal PriNciplEs uNderlyiNg The 'HiGh leVel' AspectS oF tHe nanoSyStEMs HE Proposes aNd, indEEd, HaS thoUGht IN sOMe DeTail" abouT sOmE iSsueS.