articulate vs speak

articulate is an adjective but speak is not an adjective.

Word	Noun	Adjective	Verb	Adverb
articulate	No	Yes	Yes	No
speak	No	No	Yes	No

articulate (adjective)	speak (adjective)
expressing yourself easily or characterized by clear expressive language
consisting of segments held together by joints

articulate (verb)	speak (verb)
speak, pronounce, or utter in a certain way	express in speech
express or state clearly	exchange thoughts; talk with
put into words or an expression	use language
provide with a joint	give a speech to
unite by forming a joint or joints	make a characteristic or natural sound