1. To treat (something) as if (1) it were really something else, or (2) it had qualities that it does not have (although the document was not in fact signed until April 21, it explicitly states that it must be deemed to have been signed on April 14).
2. To consider, think, or judge (she deemed it necessary).
“ ‘Deem’ has been traditionally considered to be a useful word when it is necessary to establish a legal fiction either positively by ‘deeming’ something to be what it is not or negatively by ‘deeming’ something not to be what it is…. All other uses of the word should be avoided …. Phrases like ‘if he deems fit’ or ‘as he deems necessary’ or ‘nothing in this Act shall be deemed to … ’ are objectionable as unnecessary deviations from common language. ‘Thinks’ or ‘considers’ are preferable in the first two examples and ‘construed’ or ‘interpreted’ in the third…. ‘Deeming’ creates an artificiality and artificiality should not be resorted to if it can be avoided.” G.C. Thornton, Legislative Drafting 99 (4th ed. 1996).