Why do you say "to speaking" in this phrase? The surprising secret to speaking with confidence" What is the reason to use ING at the end of the verb speak?
"To" in this construction is a preposition, not part of the infinitive of the verb. In fact the verb "speak" is not a verb at all here, but a gerund.
The construction is The secret to noun, with "to" meaning "of." Thus:
- The secret to math.
- The secret to happiness.
- The secret to speaking with confidence.
the surprising secret to speaking with confidence
In this phrase, speaking functions as a noun and is called a gerund.
gerund noun [ C ] LANGUAGE specialized UK /ˈdʒer.ənd/ US /ˈdʒer.ənd/
a word ending in "-ing" that is made from a verb and used like a noun: In the sentence "Everyone enjoyed Tyler's singing", the word "singing" is a gerund.
Further reference on the use of the form to+v+ing is shown below.