Speech (n.) was no more invented by humans than walking on two legs.
Speech (n.) with and without thought is like playing a piece of music with and without thought.
Speech (n.) can be automatic without sounding mechanical; imagine two people talking through one mouth.
Speech (n.) is full of music: a sigh, the lift of a question, the voice's countless gestures.
Speech (n.) may be called the instrument of thinking, but language does not carry thought the way the notes of a song carry its words.
Speech (n.) without thought is just speech with certain accompaniments switched off, say by pinching your skin hard while reading aloud.
Speech (n.) is learned by thinking in the language from the start; there is no stage of using it to communicate without yet thinking in it.