The most common and most likely answer to this crossword clue is the 10 letter word PREDICATES
I've seen this crossword clue in The Daily Telegraph
P
R
E
D
I
C
A
T
E
S
Buddy explains!
The straight part
We know that "Affirms/what may be said of subjects" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case affirms/what may be said of subjects = predicates.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 PREDICATES mean?
PREDICATES noun- (grammar) The part of the sentence (or clause) which states something about the subject or the object of the sentence.
- A term of a statement, where the statement may be true or false depending on whether the thing referred to by the values of the statement's variables has the property signified by that (predicative) term.
- An operator or function that returns either true or false.
- To announce, assert, or proclaim publicly.
- To assume or suppose; to infer.
- (originally United States) to base (on); to assert on the grounds of.
- (grammar) To make a term (or expression) the predicate of a statement.
- To assert or state as an attribute or quality of something.