I think Friedman's general idea is correct. For me inflation is not about individual price levels but about the potential of increased/decreased price levels. If money supply increases, it makes room for increased price levels. Without increased money supply, it would only be possible for a product price to increase if another product price decreases. In reality I think inflation already occurs when money supply is increased - it's just not priced in as it takes time for prices to adjust. However, the period of time in which the increase happens, cannot be predicted - e.g. it can be 1 year or 100 years.