Please consider the following four sentences.  1 - He finished school  2 - He has finished school  3 - He had finished school  4 - He did finish school  Do all of these sentences mean the same or not? If there are any differences, could you explain?  I'm not asking which one is more appropriate to express that someone completed his last school year. Instead, I'm just using these sentences as examples in order to understand the correct usage of each past tense form in English. Thank you.  Edit: Not a duplicate. My question considers specific past tense forms, while the suggested question deals with other unrelated tenses and aspects.
Non-na­tive speak­ers of­ten get con­fused about what the var­i­ous tens­es  and as­pects mean in English. With in­put from some of the folk here I've put to­geth­er a di­a­gram that I hope will pro­vide some clar­i­ty on the mat­ter.  I of­fer it as the first an­swer to this ques­tion. Con­sid­er it a liv­ing doc­u­ment. In­put is wel­come, and good sug­ges­tions will be  in­cor­po­rat­ed in­to the di­a­gram.    No­ta bene: What this is not is a dis­cus­sion of whether there are  more than two tens­es in English. , to which this ques­tion is not in­tend­ed to sup­ply ar­gu­ments one way or the oth­er.  Here, the aim is to pro­vide an overview of what con­struc­tions English-speak­ing peo­ple use for con­vey­ing in­for­ma­tion about ac­tions re­fer­ring to past, present, and fu­ture, and to pro­vide it first and fore­most to pre­cise­ly the peo­ple who are like­ly to use "tense" as a catch-all term in their search, rather than to lin­guists who know bet­ter.  Break­ing News There is now an ex­cel­lent ELU blog ar­ti­cle ti­tled  . It is high­ly rec­om­mend­ed read­ing.
Objective-C Static Class Level variables How to run adb and fastboot commands from Termux? How much does it cost to have a custom ASIC made? What does the colon in Tikz coordinates mean? Neutrino project in Tamil-Nadu India In , the Indian government is going to start a neutrino project.  Questions:   Is it harmful for people who stay there?   Will this project affect any living beings? Does it cause any pollution? I just saw Get Out, and there's one thing I don't understand.  Georgina turns out to be controlled by Rose's grandmother; its grandmothers brain in her body. Why then, is Georgina constantly cleaning and being treated like an actual maid.  During the diner scene, we get a glimpse into the kitchen, and we see Georgina holding up a plate in way that suggested that she was made to work and cook. The pose and the fact that she was already standing there holding the plate before Missy enters the kitchen was also quite strange and suggestive.  Also, at the "party" theres a moment that Chris sees Georgina and Missy. For a moment he thinks that Georgina is being involved in the party, but than it turns out the Georgina is just handed empty glasses to take care of.  So this I don't get. If its really grandma inside Georgina, then why is she treated in this way? Change ViewPager animation duration when sliding programmatically If $x^{2}-x\in Z(R)$ for all $x\in R$, then $R$ is commutative. If $x^{2}-x\in Z(R)$ for all $x\in R$, then $R$ is commutative.  I need to proof this theorem and I have something like this below. However, I do not know how to continue this proof.   $(x+y)^{2}-(x+y)=x^{2}+xy+yx+y^{2}-x-y=(x^{2}-x)+(y^{2}-y)+xy+yx\in Z(R)$  so $xy+yx\in Z(R)$ Easy way to disable a UITextField? Is there an easy way to disable a UITextField in code?  My app has 12 UITextField that are all turned on by default, but when a change is detected in my Segment Control I want to disable some of the UITextField depending on what Segment the user picks.  Just need to know how to disable it or make it non-editable?  Thanks Conformally Map Region between tangent circles to Disk I have recently been reading about Quantum Electrodynamics which I found very interesting, but even more confusing.  I understand photons mediate the electromagnetic force and interactions between charges can be described by virtual photon exchange. And that in Quantum Mechanics particles paths can be evaluated by sum over all paths...  An electron travelling from one point to another will take all paths, emitting and reabsorbing virtual photons. Does the electrons take all paths including those that involve faster than light velocities?  Is this question null, Does it mean anything to ask about properties of virtual particles?  Do I have the wrong idea about what virtual particles are? I want my intent to be launched when the user goes to a certain url: for example, the android market does this with  urls. so does youtube. I want mine to do that too. How do I turn on SharePoint App store in SharePoint 2013 I am getting this message when I want to add a app:     Sorry, apps are turned off. If you know who runs the server, tell them   to enable apps. Fibonacci sequence emerging from integer partitioning I have a Python module installed on my system and I'd like to be able to see what functions/classes/methods are available in it. I want to call the help function on each one. In Ruby I can do something like ClassName.methods to get a list of all the methods available on that class. Is there something similar in Python? eg. something like: from somemodule import foo print(foo.methods)  # or whatever is the correct method to call Where can a tourist apply for a UK Visitor (standard) Visa? Window title in bottom of Activities overview is not visible when opening multiple windows When should I make my players actually roll for stuff? I've tried to focus my group heavily on Role Playing, perhaps too well given some of my recent problems, which are Orthagonal, and linked mostly to provide historical context.        A lot of the answers to these questions revolve around "have off the rail's multiple angles" and "don't make people roll for information they must have". That seems well understood to me at this juncture, in fact I have been doing just that, and I think it's causing some other problems.  I have only rarely made people roll for anything (combat aside) anymore, unless it's absolutely non critical. I try to get the players to Role Play their investigations and give them information when they look in the right places, and their are multiple right places.  This results in skills, especially social/mental, being completely inessential, and players not gaining important information because they aren't poking around the right area at all, or asking people who aren't interested in talking to them because they're currently a bunch of random Joe's.  The players aren't stuck at this time, I'm just trying to get better and not have functionally dead scenes, that don't rely on the players to play "what is the GM thinking" nor do I want to just give them every answer.  The reality is, I'm not sure when to make them roll to find things out. what criteria? or other advice, can I use to decide that the players are better off making a Roll to move forward than to purely use Role Playing?  update This question focuses on the Social and to a lesser degree Mental aspects, as it's usually pretty easy to tell when a Physical Roll is needed, even out of combat. It's harder to tell when to make people roll for things they can talk their way through.  I'm playing World of Darkness 2nd Edition, but answers not specific to that are welcome. I initially thought that dark energy must in some way violate conservation of mass and energy since the component of the energy density of space that comes from dark energy is constant, and space is expanding. Therefore, as space expands the energy in the universe that comes from dark energy would increase. I presumed the source of this energy was not coming from the conversion of other types of energy to dark energy, so it must violate conservation.  I decided to Google this and came upon this article:    It says that dark energy does NOT violate conservation and quotes Carroll, Press, and Turner (1992):  "…the patch does negative work on its surroundings, because it has negative pressure. Assuming the patch expands adiabatically [i.e. without loss or gain of heat], one may equate this negative work to the increase of mass/energy of the patch. One thereby recovers the correct equation of state for dark energy: P = – ρ c2. So the mathematics is consistent."  Is there a way to explain this in layman's terms? (The blog attempted to do this, but it was very unclear to me.) More specifically, can you explain where my initial train of thought described above fails when I erroneously concluded that dark energy violates conservation?  Thank you. Does it just vanish into space leaving nothing behind or does it expel some material?    Also, talking more about black holes, as far as I understand the term "temperature", it is defined by the amount of kinetic energy of the particles of a body and from what I have read, there are no particles inside a black hole, I know that you can find the temperature of a black hole by analyzing its Hawking radiation but I cant really understand how the term "temperature" can be applied to a black hole. Does it mean that whatever is that it is inside a black hole has kinetic energy? Have physicist already experienced the death of any regular black hole (by regular I mean space-sized black holes not micro ones created in labs)? Also, where is the Hawking radiation form? Because if it is released by the black hole I bet it must have formed outside the event horizon, but how exactly?