I buy & sell postcards as part of my business, I don't really collect them. But I look closely at every one. I'm forced to consider a lot of technical things about the condition and era of the card, and I have to look at it with an eye to what I think its likelyhood of selling is. I have to store them, retrieve them, manage them. That's part of my job, the job I tell myself I do so I wont have to get a real job. I've handled thousands of postcards, just this year.
I really like them, and here's why.
I don't know if they are social history, but they sure are social commentary. The subject of the card itself immediately tells you what someone considered important - sometimes you wonder why, but there is a reason for it. Its a structure, or art, or a beautiful scene, or an animal, or something funny, or maybe patriotic. But its your first clue to what someone, or some group considered important. These things were made to sell, so they had to appeal to potential buyers.
The caption on back (if there is one) gives more clues about the times. The way its written - many older ones are verbose, and written passively. Many cards, especially older ones, will tell the cost of whatever is on the picture, or the speed or the height or some statistic meant to impress people. I had once had an old postcard of the Woolworth Building in New York City, which made sure you knew how tall it was and that it was the tallest building in the world at the the time.
Some of these cards are used - most of the people who wrote or recieved these cards are long gone. Sometimes a group of cards come form the same batch, and you can follow the family along for a spell, sometimes years - watch the son's travels, his marriage, his carreer, as he sends postcards back to his parents. And I realize the reason I eventually ended up with them is because someone, most likely the person the cards were sent to, has died. It makes me wonder.
I recently sold a group of old cards - the oldest I've had yet. They dated from 1886 to around 1908, and they were blank Pre-Paid postcards. No pictures, you wrote an address on one side, and your message on the other. All these cards were going back and forth to the same people in New England - Vermont and New Hampshire. When I was groing up, there were lots of people alive who were born in and remembered the 19th century. They were quite old, I was quite young, and I reckon I thought they were born old. Well this group of 20 cards or so drove home to me that these 19th century people had feelings, not too different than mine or anyone elses. They loved their parents, wrote to their grandparents, worried about their children, and struggled to get by. In one card, a mother was worried because her daughter, who had recently been exposed to the measles, was not feeling well. This was in 1886 (or maybe 1892), and was a serious thing. On another card, some one wrote that she could hear "Papa in the kitchen cracking nuts". Were they walnuts? If so they were black walnuts, very, very flavorful. She didnt say, but when I read that, I could hear it too. I could imagine it, I could see it plain as day. Another was worried because they needed to get the hay in and they couldn't because it was raining and had been raining for a couple of days. There is a bit of despair in that one, because it was probably quite serious to them if they could not get the hay in. And in another the writer was worried because they wanted to go pick up their daughter (I think), but couldn't because "the horse is lame yet". The people who wrote these messages, are dead. The people they worried about, cared for, loved, are also dead. Their concerns & problems no longer matter. There's a good chance that everything they were familiar with has changed. But these little cards brought it home to me that they were real, they were very human, they existed and struggled with their fortunes in life, and had feelings and problems just like I do, and everyone I know does. And that too, makes me wonder.