<HTML><FONT FACE=arial,helvetica><FONT SIZE=2>To distinguish it from the emphatic "can NOT"?
<BR>e.g. A) "She cannot sing." [neg. ASSERTION]
<BR> vs.
<BR> B) "She can not [NOT] sing." (1.DENIAL [She does not have my
<BR>permission to
<BR> do so] or 2. DISAGREEMENT [I disagree with your assertion that she
<BR>can.])
<BR>
<BR>I think, thus, that this spelling distinction (cannot/can not) reflects, or,
<BR>rather, parallels the pragmatic distinction between asserted (new) vs.
<BR>presupposed (familiar) information and, most importantly, the scope of
<BR>negation. In (A), the scope is the lexical verb, "sing." The presupposed or
<BR>familiar information, the subject "she," is not included; only the singing is
<BR>under the scope of negation . The subject, "she," might have the ability, or
<BR>permission, to do engage in other activities. In (B), the scope of negation
<BR>is ambiguous in that its boundary can be any or all of the affirmative
<BR>statement [both presupposed and asserted information]. Consequently, the
<BR>scope of negation can be either the presupposed information [subject,
<BR>"she,"] as in, NOT She can sing [Someone else is able to or has permission
<BR>to'], or the entire proposition [The speaker disagrees with the assertion
<BR>that "she" can sing], or only the new, asserted information, e.g. NOT can
<BR>sing [The subject either does not have the ability or has not been granted
<BR>permission to do so]. </FONT></HTML>