LUCID

clear, easily understood

(of language) transparently clear
SYN - crystal clear, pellucid, perspicious
"pellucid prose"

having a clear mind
"a lucid moment in his madness"

capable of thinking and expressing yourself in a clear and consistent manner
SYN - coherent, logical
"a lucid thinker"

"It was really important for him that he be in a relationship with someone who was lucid."

"He was in a terrible place after he got dumped and it was near impossible for him to be lucid."

"What made him such a great leader and teacher was his ability to be so lucid about such convoluted and confusing subjects."