Hasta donde yo se son perfectamente sinónimos. Creo que en el único caso en el que se usa "utilizar" en vez de "usar" es cuando nos referimos a una persona. Cuando la utilizamos para obtener algún beneficio, para aprovecharnos de ella. Ej: Utilicé a mi amigo para conseguir el trabajo Aunque si dices "usé a mi amigo para conseguir el trabajo" se te entiende igual. Es cuestión de hablar siguiendo las normas. Un saludo. Airam

Both are synonymous. You can use them both. The difference is: "Utilizar" is something that is useful to you, IE, you have a benefit from that. EG. Utilicé mi pierna para sacar mi cartera debajo del coche. (your leg was useful for you, but that doesn't mean it's made for that.) "Usar" is something that you are using and it is made ​​for that. EG. Usé mi computadora para escribirle a mi amigo. (you used your computer, because the computer is made for that. Have a nice day!

Hi, in the daily speak of native speakers there's almost any difference between them, eventhough of it, explanations made before are correct. But when you're spoken with native speakers, it's sure that they'll understand you, if you use "utilizar" or "usar". For example: "Voy a usar una gorra mañana" and "Voy a utilizar una gorra mañana" in fact means the same thing.

Hi, I would tell you to feel free to use both words as synonyms. Most of Spanish speakers people will understand you. Regards

Really I must say that two words are similar meaning in common usage in Spanish, so that they can be practically considered as synonyms. Nevertheless, if we look for some very small difference in possible meaning, we could say that "UTILIZAR" refers to the idea of the use or employment of something or someone with the idea of find it "useful". On the other hand, we could suggest that "USAR" mainly refers to the use of doing something or the habit or doing something, regardless of their value or utility. As examples we would say: "Necesito UTILIZAR gafas para leer" (utility) "No me gusta USAR las gafas todo el día" (use)