Cogerle del brazo = grab him by the arm Cogerle de un brazo = grab him by an arm Coger a Julio por un brazo = it doesn't sound very nice. It's right but not pretty. Anyway as Rocio well said, "cogidos del brazo" is an idiom meaning the posture where a romantic couple may walk side by side or how the father brings the bride to be to get married (I hope this examples help you picture it) Just a tiny piece of advice. Feel free to use "coger" in Spain as we only use that verb in this sense but don't do it in Latin America as its main meaning is to f**k. P.S.: I'm Spanish

Hola Richard. Here my answers: In this case the prepositions "de" (de+el) and "por" both refer that we are grabing Julio from an specific part of the body, in this example by the/an arm. For me the following sentences have the same meaning: Cogerle del/de un brazo Cogerle por el/por un brazo Coger a Julio del/de un brazo Coger a Julio por el/ por un brazo *In the first two sentences we use the direct object pronoun "coger-le" instead of "a Julio". So this has nothing to do with the use of the prepositions. ¡Saludos!

Cogerle del brazo = La dama cogía a su marido del brazo (Los dos iban juntos). The lady took her husband's arm (The two went together). Coge a Julio por un brazo = Agárralo por el brazo Grab him by the arm