The most common and most likely answer to this crossword clue is the 10 letter word SUBJECTIVE
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "expressing personal ideas" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expressing personal ideas = subjective.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SUBJECTIVE mean?
SUBJECTIVE adjective- Formed, as in opinions, based upon a person's feelings or intuition, not upon observation or reasoning; coming more from within the observer than from observations of the external environment.
- Pertaining to subjects as opposed to objects (A subject is one who perceives or is aware; an object is the thing perceived or the thing that the subject is aware of.)
- Resulting from or pertaining to personal mindsets or experience, arising from perceptive mental conditions within the brain and not necessarily or directly from external stimuli.
- Lacking in reality or substance.
- As used by Carl Jung, the innate worldview orientation of the introverted personality types.
- Experienced by a person mentally and not directly verifiable by others.
- (grammar) Describing conjugation of a verb that indicates only the subject (agent), not indicating the object (patient) of the action. (In linguistic descriptions of Tundra Nenets, among others.)