Pensative.
A notion is a thought, idea, or impulse.
The word rethink is a verb. Definition is reconsider. The most common use of the this word is have a second thought, or take another look, or think it over. This is a very useful word as a whole.
Another word for the time that was dubbed the Age of Reason would just be the Enlightenment. This was a period during the 17th and 18th centuries that was a societal reformation. There was progress made in science, art, and faith, as well as knowledge and scientific thought.
Yes, the noun 'thought' is an abstract noun, a word for something that takes place in a person's mind; a word for a concept.
Thoughtful is not an adverb, a word that modifies a verb, an adjective, or another adverb. It's an adjective, a word that describes a noun. Example: Kendra is a thoughtful person. The adverb form is thoughtfully.
Busy, distracted, absorbed, engaged, immersed, engrossed, rapt, lost in thought, oblivious...
pondered
Mesmerised, absorbed, captivated, entranced, fascinated, enraptured, beguiled...
Idea
self thought
thought of
To be meditative. Absorbed in thought.
A notion is a thought, idea, or impulse.
Respect, concern, deliberation, thought.
Options includeMull [over]DeliberatePonderPlanAnalyzeBrainstorm
A writer uses the word "but" for a few reason. The word "but" can be used in a sentence easy or it can add on another thought.
Another word is spirit. It is thought by some that when people die, their spirit goes to be with their god.