Well, after reading the previous reply, I feel a little tangled. In fact, LZ is right. V can be changed in a short period of time. The best answer before is absolutely because this guy is a junior in economics. It is true that V is considered to be unchanged for a long time (of course, so is Y), but when Friedman reinterprets the concept of monetarism, he thinks that this V can be changed, but the change range is very small. In addition, for the old monetarists, the change direction of this V is suitable for the same direction of currency change, that is, it will increase the range of currency change (although it still has little impact).

Well, I don't know how China's textbooks are taught, but I think this book is a little fussy about LZ. The first theory is correct and can indeed support the statement that money affects real variables in the short term, but the second theory is a bit vague. The possible explanation is this. In Keynesian theory, those Keynesians think that, first of all, V is very unstable (note that it is very unstable), and then, in some cases, monetary policy will become very ineffective, that is, in those two special cases, one is in a liquidity trap (like what is called liquidity preference, there is no way, English learners don't know how to translate Chinese). The other is that the relative benefit of investment is inflexible, which can also be called investment trap. In both cases, the money supply will increase or decrease, which has no effect on actual output or real income. At this time, Keynesians believe that the reverse change of V absorbs some changes in the money supply (that is, in the opposite direction to the change of the money supply), so that the nominal national income on the other side of the equation has no influence.

I think the second theory means that V can change slightly (without absorbing the influence of currency changes, of course, for traditional monetarists, this V changes in the same direction as currency changes). This ensures that changing the money supply in a short time will have an impact on the nominal national income (unlike the Keynesian hypothesis mentioned earlier).

Then add that don't look at the transmission mechanism in a hurry. This transmission mechanism has limitations. In monetarism, we study how to influence variables in all directions. The most important thing is to use AD-AS model to turn this curve into what is happening. Long-term AS is a vertical line, and the final output Y (or national income) of this advertisement will remain unchanged no matter how we change it. If the money supply increases, it will lead to the increase of ad, and if this intersects with the short-term AS curve, it will find that the output or income Y increases slightly, which LZ wants to know. In the short run, the increase of money can affect output (due to money illusion), and then in the long run, as we discussed before, the intersection with vertical As will only change the price level, but not the output or income Y.

Three years ago, I don't know if I have made it clear now. This is just my humble opinion. I hope it helps. . . I'm really sorry. I just graduated from high school three years ago, and I can't answer this question even if I see it. . .