-- For Ability — if it's
about ability, "talk" is preferred: "cats
can't talk", "when I'm drunk I lose my ability
to talk". Note
that "speak" is allowed but is less popular;
-- For Languages — use "speak":
"I speak English";
-- For Action — covered
in answers above; both words can be used; "speak" is
mostly about single-direction, while "talk" usually
refers a conversation (and is less formal);
-- To Express
information — use "say" or "tell":
"I told her that I love her". Here, "I
love her" is the information being expressed. "Say"
can also be used, but it connotates a single-time action. Compare: "I said that
the discussion is over and hung up the phone."
-- Imperative usually
follows the rules above, but due to an extended popularity, here's a brief:
· Extended time or dialogue — "Talk to
me."
· Long monologue — "Tell me
about your problem."
· Short monologue — "Say something!"
· Requesting a certain attribute
of speaking process — "Speak slowly
please."
FOR A CLEARER VIEW:
ADAPTADO DESDE: www.languagelearningbase.com
