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Sometimes I think:  
～とも came from ～と思う  
～かしら came from ～かしらん（知らない）

It's possible I'm wrong, so I would like to know the real meaning of those
suffixes. Also, I'd like to know when I can use them without any problem (when
talking about spoken language).

Ex:

  * もちろんいいとも 
  * 明日は雨かしら
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2011-06-27T14:09:23.907
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2012-05-29T22:19:59.157
2012-05-29T22:19:59.157
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question
usage etymology
What are the meanings of ~とも [tomo] and ~かしら [kashira]?
～とも (in the sense you seem to be talking about) is a rather archaic sentence-
final particle which is used for strongly asserting something that the
listener may not be so sure about. That makes it similar to the far more
colloquial particle よ, but it's somewhat stronger and more decisive than よ.
「いいとも」, for instance, would usually come in the context where A asked B
whether it's okay to do something, and B wants to firmly reassure A that it's
okay.

This とも has no relation whatsoever with ～と思う, but rather comes from combining
the particles と and も. かしら, on the other hand, indeed comes from かしらん
(＝かしらない), as Dave has already indicated.
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2011-06-27T21:05:54.780
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2011-06-28T16:19:58.633
2011-06-28T16:19:58.633
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answer