{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2023,2,20]],"date-time":"2023-02-20T19:32:41Z","timestamp":1676921561355},"reference-count":6,"publisher":"Cambridge University Press (CUP)","issue":"1","license":[{"start":{"date-parts":[[2014,3,12]],"date-time":"2014-03-12T00:00:00Z","timestamp":1394582400000},"content-version":"unspecified","delay-in-days":17086,"URL":"https:\/\/www.cambridge.org\/core\/terms"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["J. symb. log."],"published-print":{"date-parts":[[1967,6]]},"abstract":"<jats:p>The presence of a rule for existential instantiation (EI) in a system of natural deduction often causes some difficulties, in particular, when it comes to formulate necessary restrictions on the rule for universal generalization (UG). A system containing rules for EI and UG that avoided Quine's rather cumbersome restrictions on these rules was formulated by Copi [2], but the system was found to be inconveniently restrictive. A less restrictive system was therefore suggested by Copi [3]. Also that system forces some deductions to be unnecessarily long as is shown in Prawitz [5, Appendix C, p. 104], where a way to liberalize Copi's restriction on UG is suggested (p. 105). However, the system suggested by Copi [3] is also incorrect (i.e. unsound) as has recently been shown by Parry [4] in this Journal.<\/jats:p>","DOI":"10.2307\/2271245","type":"journal-article","created":{"date-parts":[[2006,5,6]],"date-time":"2006-05-06T16:38:11Z","timestamp":1146933491000},"page":"81-82","source":"Crossref","is-referenced-by-count":3,"title":["A note on existential instantiation"],"prefix":"10.1017","volume":"32","author":[{"given":"Dag","family":"Prawitz","sequence":"first","affiliation":[]}],"member":"56","published-online":{"date-parts":[[2014,3,12]]},"reference":[{"key":"S0022481200114574_ref006","volume-title":"Logic for mathematicians","author":"Rosser","year":"1953"},{"key":"S0022481200114574_ref004","first-page":"119","volume":"30","author":"Parry","year":"1965","journal-title":"Comments on a variant form of natural deduction"},{"key":"S0022481200114574_ref002","volume-title":"Symbolic logic","author":"Copi","year":"1954"},{"key":"S0022481200114574_ref001","doi-asserted-by":"publisher","DOI":"10.1007\/BF02548936"},{"key":"S0022481200114574_ref003","first-page":"52","volume":"21","author":"Copi","year":"1956","journal-title":"Another variant of natural deduction"},{"key":"S0022481200114574_ref005","volume-title":"Natural deduction. A proof-theoretical study","author":"Prawitz","year":"1965"}],"container-title":["Journal of Symbolic Logic"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.cambridge.org\/core\/services\/aop-cambridge-core\/content\/view\/S0022481200114574","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2019,6,2]],"date-time":"2019-06-02T16:04:52Z","timestamp":1559491492000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.cambridge.org\/core\/product\/identifier\/S0022481200114574\/type\/journal_article"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1967,6]]},"references-count":6,"journal-issue":{"issue":"1","published-print":{"date-parts":[[1967,6]]}},"alternative-id":["S0022481200114574"],"URL":"https:\/\/doi.org\/10.2307\/2271245","relation":{},"ISSN":["0022-4812","1943-5886"],"issn-type":[{"value":"0022-4812","type":"print"},{"value":"1943-5886","type":"electronic"}],"subject":[],"published":{"date-parts":[[1967,6]]}}}