In the streets see alternative groups (5)
I believe the answer is:
sorts
'groups' is the definition.
The answer and definition can be both related to thinking as well as being plural nouns.
Maybe you can see a link between them that I don't see?
'in the streets see alternative' is the wordplay.
'in the' means one lot of letters goes inside another.
'streets see' becomes 'sts' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'alternative' becomes 'or'.
'sts' going around 'or' is 'SORTS'.
Can you help me to learn more?
(Other definitions for sorts that I've seen before include "Classifies" , "Systematically arranges" , "classes" , "Arranges in correct or desired sequence" , "Categories" .)