Category to give you the name of a property from a selector, will assert that the property exists.

DCTPropertyNameFromSelector.h

#import <Foundation/Foundation.h>

@interface NSObject (DCTPropertyNameFromSelector)
- (NSString *)dct_propertyNameForSelector:(SEL)selector;
@end

DCTPropertyNameFromSelector.m

#import <objc/runtime.h>

@implementation NSObject (DCTPropertyNameFromSelector)

- (NSString *)dct_propertyNameForSelector:(SEL)selector {
	NSString *string = NSStringFromSelector(selector);
	
	BOOL hasProperty = NO;
	unsigned int outCount;
	objc_property_t *properties = class_copyPropertyList([self class], &outCount);
	for (unsigned int i = 0; i < outCount; i++) {
		objc_property_t property = properties[i];
		const char *propName = property_getName(property);
		NSString *propertyName = (propName != NULL) ? [NSString stringWithCString:propName encoding:NSUTF8StringEncoding] : nil;
		hasProperty = [propertyName isEqualToString:string];
		if (hasProperty) break;
	}
	free(properties);
	NSAssert(hasProperty, @"%@ does not have a property named %@", NSStringFromClass([self class]), string);
	return string;
}

@end

main.m

#import <Foundation/Foundation.h>
#import "DCTPropertyNameFromSelector.h"

@interface Test : NSObject
@property (copy) NSString *string;
@end
@implementation Test
@end

int main(int argc, char *argv[]) {
	@autoreleasepool {
		Test *test = [Test new];
		NSString *propertyName = [test dct_propertyNameForSelector:@selector(strings)];
		NSLog(@"%@", propertyName);
	}
}