【Thoughtful】 ,  【reflective】 ,  【speculative】 ,  【contemplative】 ,  【meditative】 ,  【pensive】  can be applied to persons or their moods, attitudes, expressions, and utterances as meaning characterized by or showing the power to engage in thought, especially in concentrated thinking.

【Thoughtful】 may imply either the act of thinking concentratedly or the disposition to apply oneself to the careful and serious consideration of problems or questions at issue.

【Reflective】  differs from  【thoughtful】 in its stronger implication of orderly processes of thought, such as analysis and logical reasoning, and in its suggestion of a definite aim, such as the understanding of a thing's nature or of its relation to other things or the reaching of a definite conclusion.

【Speculative】 implies a tendency or inclination to think about things of which direct knowledge is either impossible or so limited that any conclusions are bound to be uncertain.

Hence the term often implies theorizing or conjecturing without consideration of the evidence or with little attention to the evidence.

【Contemplative】 carries a stronger implication than the other words of an attention fixed on the object of one's thoughts; it may imply as its object something perceivable by the senses or something abstract yet comprehensible by the mind, or it may suggest a habit of mind.

【Meditative】  , except in religious use, where it comes very close to  【contemplative】 , usually implies a tendency to ponder or muse over something without necessarily implying any such intellectual purpose as understanding a thing or reaching a conclusion regarding it.

The term therefore often comes close to  【thoughtful】 , though it usually implies some consecutive reasoning and sometimes suggests pleasure rather than seriousness in the exercise of thought.

【Pensive】  is not always clearly distinguishable from  【meditative】 , though at times it carries a stronger suggestion of dreaminess, of wistfulness, or of melancholy.