The most common and most likely answer to this crossword clue is the 9 letter word INDUCTIVE
I've seen this crossword clue in Independent
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Buddy explains!

The straight part
We know that "following certain reasoning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case following certain reasoning = inductive.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.
Crossword Answer definitions
INDUCTIVE adjective- Of, or relating to logical induction.
- Of, relating to, or arising from inductance.
- Introductory or preparatory.
- Influencing; tending to induce or cause.