When debating options—like whether to take public transit or drive to work—you need tools to organize your thoughts and contrast different points.
On one hand... on the other
To weigh pros and cons, use por un lado (on one hand) and por otro lado (on the other hand). In everyday speech, it is very common to drop the second lado and just say por otro.
| On the one hand I like driving, but on the other I hate traffic. | Por un lado me gusta manejar, pero por otro odio el tráfico. |
| On the one hand you will gain time, but on the other you will spend a lot. | Por un lado ganarás tiempo, pero por otro gastarás mucho. |
You can also use the full phrase to clearly emphasize the contrast.
| On one hand, the car is fast; on the other hand, the disadvantage is the traffic. | Por un lado, el carro es rápido; por otro lado, la desventaja es el tráfico. |
Expressing contrast with "en cambio"
When you want to show a direct contrast between two things, use en cambio. It translates closely to "however," "in contrast," or "on the other hand." Notice how it often follows a semicolon when separating two complete, contrasting thoughts.
| The bus is cheap; on the other hand, the train fare will cost more. | El autobús es barato; en cambio, el pasaje del tren costará más. |
| The train is frequent; in contrast, the fare is expensive. | El tren es frecuente; en cambio, el pasaje es caro. |
Structuring a full argument
For a neatly structured argument, you can start your point with por un lado and introduce the opposing viewpoint with en cambio.
| On the one hand, the train is eco-friendly; however, the car pollutes a lot. | Por un lado, el tren es ecológico; en cambio, el carro contamina mucho. |