I swear TO it > "I am telling the truth!" Example: A gorilla visited me last night. Really. I swear to it! I swear BY it > "I really think it is effective/useful" Example: I swear by taking a walk after dinner each evening. Very good for the digestion. You can also swear ON something: taking an oath/swearing on the bible in court/on your life even. Maybe I can try putting the 3 together? "I swear ON my life that the after-dinner walk I swear BY is beneficial to me. Honestly! I swear TO it!" Er, I think someone can think of better sentences!

The phrases "swear by" and "swear to" are both correct, but they have different meanings and uses. Here’s how they differ: Swear by: Meaning: To strongly believe in the effectiveness or reliability of something, often based on personal experience. Usage: You use "swear by" when you're endorsing something or someone. Example: "I swear by this brand of coffee; it’s the best I’ve ever had." Swear to: Meaning: To make a serious or solemn promise or statement, often invoking something or someone as a witness. Usage: You use "swear to" when you’re making a promise or affirming something. Example: "I swear to tell the truth, the whole truth, and nothing but the truth." Summary: Use "swear by" when you’re vouching for something’s effectiveness or reliability. Use "swear to" when you’re making a serious promise or declaration.

Eu juro !!! Não fiz isso = I swear to God! I swear by: to believe strongly that something is effective or useful: My dad swears by these vitamin pills. = Meu pai jura que essa vitamina funciona

"I swear __ aerobic exercise! It makes me fit. I don't care if you believe me. And I don't care what it does for you. For me, it's great." "I told you the truth. Honestly. I swear __ it! Please believe me." Robson, make your choices: TO or BY ? I've replied to your comment. Does it help yet?