A rider calls from the gate with your parcel, you are three floors up, and you tell him เอาไปให้ยาม (ao bpai hâi yaam). He rides off and leaves it with the guard. That is exactly what you said. เอาไป is take it away from where I am, and if what you wanted was for him to bring it up, the word was เอามา (ao maa). One syllable on the back of the verb decided which of you moved. English marks this on a handful of verbs, come against go, bring against take, and leaves the rest of them blank. Thai marks it on every verb of movement, which is why the mistake survives for years and why learners keep having conversations in which everybody is polite and nobody ends up where they meant to be.
Thai hangs a direction on the back of a verb, and the direction is not read off a map. It is read off the speaker. ไป (bpai) points away from where the speaker is standing at the moment of speaking; มา (maa) points towards it. This is why the same staircase gets two different words depending on who is talking: the rider standing in your lobby says ลงมารับหน่อยได้ไหมครับ (long maa ráp nàwy dâi mǎi khráp), come down and take it, because you would be moving towards him, and you reply กำลังลงไปครับ (gam-lang long bpai khráp), on my way down, because you are moving away from where you are. One man, one set of stairs. Neither speaker is wrong, and neither could use the other one's word. When somebody speaks to you, then, มา points at them, which is the practical form of the rule you will use most on the phone.
Before any of that, ไป and มา are ordinary verbs in their own right, and they keep that job: ไปตลาด (bpai dtà-làat), go to the market, มานี่ (maa nîi), come here. From there they take two positions against another verb, and the two mean different things. In front of the other verb they mean go and do it, or come and do it: พรุ่งนี้จะไปหาหมอ (phrûng-níi jà bpai hǎa mǎw), tomorrow I am going to see the doctor; ออกมารับหน่อยได้ไหมคะ (àwk maa ráp nàwy dâi mǎi khá), come out and take it. Behind the other verb they are the direction of the action itself, and that is the system this lesson is about: เดินไป (doen bpai), ส่งมา (sòng maa), ยกขึ้น (yók khêun), วิ่งออก (wîng àwk).
The position is not a matter of taste, and it fits the ordering rule set out in the lesson on past, future and already: everything that sets an action up sits in front of the verb, everything that reports on the action sits behind it. Directions report, so they sit behind, and they sit there before แล้ว. เขากลับไปแล้วครับ (khǎo glàp bpai láew khráp) is built by that rule, and so is กำลังจะออกไปแล้ว (gam-lang jà àwk bpai láew), where กำลัง and จะ set the action up in front and ไป reports on it from behind. Note also what a direction is not. It is not a tense. เอามา does not mean he brought it, it means bringing towards me, whenever that happened. The time still comes from a time word, from แล้ว, or from nothing at all.
Take the pairs you need this week as pairs, because a direction word only means anything against its opposite. กลับ (glàp) is to return, and the direction splits it: เขากลับไปแล้ว is he has gone back, away from here, which is what a shop assistant tells you about a colleague, while เขาให้กลับมาใหม่พรุ่งนี้ (khǎo hâi glàp maa mài phrûng-níi) is what the immigration counter told you, come back here again tomorrow, the clerk saying มา because the counter is where she is. ส่ง (sòng) is to send: ส่งไปให้เขาแล้วครับ (sòng bpai hâi khǎo láew khráp), I have sent it on to him, against ส่งรูปมาให้ผมด้วยนะครับ (sòng rûup maa hâi phǒm dûay ná khráp), send me the photo as well. โทร (thoo) is to phone: โทรไป is the call going out from me, to you or to anybody else, โทรมา is the call coming in to me, so เมื่อเช้าเขาโทรมา (mêua-cháo khǎo thoo maa) says he called me this morning without naming anybody twice. เดิน (doen) is to walk: เดินไปข้างหน้า (doen bpai khâang-nâa), go on ahead, against เดินมาทางนี้ (doen maa thaang níi), walk over this way. In each pair the verb does the same physical thing. The direction decides who is expected to move.
Two of those verbs have a front-position twin that a household runs on. Behind the verb, ส่งไป sends a thing away from you. In front of it, ไปส่ง (bpai sòng) is go and drop somebody off: เดี๋ยวไปส่งนะครับ (dǐao bpai sòng ná khráp), let me take you home, which the phrase page on dating and family notes covers walking them to the taxi as much as riding the whole way. Its partner is ไปรับ (bpai ráp), go and fetch them, and มารับ (maa ráp) when they are the ones coming for you. One verb also changes with the passenger: เอา is for things, and a person or an animal takes พา (phaa). พาหมามาให้หมอดูหน่อยครับ (phaa mǎa maa hâi mǎw duu nàwy khráp) is how you open at the vet, and พาไปโรงพยาบาล (phaa bpai roong-phá-yaa-baan) is how you ask for somebody to be taken to hospital. The direction rule is identical, พาไป away from me and พามา towards me; only the verb changes. Using เอา of a person is worse than clumsy, and the dating and family page says why: it doubles as crude slang.
Because ให้ (hâi) so often follows in the same sentence, learn the whole shape once: verb, then direction, then ให้, then the person, then the softener, then the particle. ส่งมาให้ผมหน่อยครับ (sòng maa hâi phǒm nàwy khráp) fills all six slots. The lesson on hâi and its six jobs gives you the rule for choosing between มา and ไป there, and the verbs it applies to: ส่ง, เอา, โอน, ฝาก, บอก, ขาย, คืน, จ่าย. What is worth adding here is the slot that disappears. When the person is you, Thai leaves them out: ส่งมาให้หน่อยครับ has no ผม in it anywhere, and มา carries the whole of to me on its own. Take ผม out and the sentence still works. Take มา out and nobody has been named as the endpoint at all.
ขึ้น (khêun) and ลง (long) are up and down, and they behave the same way. Literally they are what you would expect: เดินขึ้น (doen khêun) walk up, วางลง (waang long) set down. The use you need on your first day is not literal enough to guess, though. ขึ้น is the verb for getting onto a vehicle and ลง is the verb for getting off one, whether it is a bus, a train, a motorbike or a plane. ขึ้นรถเมล์สายยี่สิบห้า (khêun rót-mee sǎai yîi-sìp-hâa) is take bus twenty-five, where สาย is the route number, and ขึ้นเครื่อง (khêun khrêuang) is to board the plane. Coming the other way, ลงป้ายหน้า (long bpâai nâa) is getting off at the next stop. The boat is the one that does not mirror cleanly, because you step down into it: ลงเรือ (long reua) is normally heard as boarding, so when you mean getting off, say ลงจากเรือ (long jàak reua). ลงจาก does the same job anywhere a bare ลง could be taken the wrong way, as in ลงจากรถ (long jàak rót). Motorbikes have their own wording. ขึ้น works on the machine, but the sentence you will actually hear is นั่งวินไปดีกว่า (nâng win bpai dii-gwàa), you would be better off taking a motorbike taxi, from the phrase page on asking directions, where วิน is both the numbered rank at the mouth of the soi and the ride itself. Riding behind somebody has its own verb, ซ้อนท้าย (sáwn tháai), so two of you on one bike is นั่งซ้อนท้าย (nâng sáwn tháai). None of this disturbs the prepositions in the lesson on saying where things are: ขึ้น and ลง are the verbs for boarding and getting off, while บน and ใน are the words for where you are once you are aboard.
The second job of ขึ้น and ลง is to put a change on a scale, and the lesson on comparing things works through that in full. What belongs here is why it is the same word. ขึ้น is upward movement whether the thing moving is a body or a number, so ดีขึ้น (dii-khêun) is better than before and ค่าเช่าขึ้นทุกปี (khâa-châo khêun thúk bpii) is the rent goes up every year. Put ขึ้น in front of ราคา instead and somebody is doing the raising: ร้านขึ้นราคาแล้ว (ráan khêun raa-khaa láew), the shop has put its prices up, against แพงขึ้น (phaeng-khêun), where the price simply rose. ลง is the mirror: อาการแย่ลง (aa-gaan yâe long) the condition got worse, ปวดน้อยลง (bpùat náwy long) hurting less.
เข้า (khâo) is in and ออก (àwk) is out, and each takes ไป or มา behind it to say which side of the doorway you are on. เข้าไป is go in, away from me; เข้ามา is come in, towards me; ออกไป is go out, away from me; ออกมา is come out, towards me. ใส่แบบนี้เข้าไปได้ไหมคะ (sài bàep-níi khâo bpai dâi mǎi khá), can I go in dressed like this, is what you ask at the foot of the temple steps, and it takes ไป because the hall is away from you. ที่อุดฟันหลุดออกมาครับ (thîi ùt-fan lùt àwk maa khráp), my filling has come out, takes มา because it came out towards the world you are standing in.
Then there are the compounds where nobody is going through a door at all, and they include some of the most common words in the language. เข้าใจ (khâo-jai) is understand, literally to enter the heart. เข้างาน (khâo ngaan) is to arrive at work, which is why วันนี้จะเข้างานสายครับ (wan-níi jà khâo ngaan sǎai khráp) is the message you send before you are due rather than when you walk in. เลื่อน (lêuan) is the ordinary word for shifting a fixed date, and on its own it does not say which way it moved, though in an office message it is nearly always later. The pair that settles it is built out of this lesson: เลื่อนออกไป (lêuan àwk bpai) pushes it back with no new date attached, and เลื่อนเข้ามา (lêuan khâo maa) pulls it inwards towards now. ออกกำลังกาย (àwk gam-lang gaai) is to exercise, putting strength out of the body. And ออก has a family of its own in the negative, where ไม่ออก means you cannot manage to get the thing out: หายใจไม่ออก (hǎai-jai mâi àwk) cannot breathe, one of the phrases to have ready for a 1669 ambulance call, นึกไม่ออก (néuk mâi àwk) cannot bring a name to mind, พูดไม่ออก (phûut mâi àwk) lost for words, อ่านไม่ออก (àan mâi àwk) cannot read it. One warning inside this group. ออกงาน (àwk ngaan) is not the opposite of เข้างาน, it means going out to a function. Finishing work for the day is เลิกงาน (lôek ngaan), and leaving the job altogether is ออกจากงาน (àwk jàak ngaan).
There is also a second ไป that is not a direction at all, and it lands in the same slot. Behind a quality word it means too much: แพงไป (phaeng bpai) too expensive, เค็มไป (khem bpai) too salty, and the softened แพงไปหน่อย (phaeng bpai nàwy) that opens a negotiation, all worked through in the lesson on degrees. The test is what sits in front of it. A verb of movement in front means direction; a quality word in front means the amount has gone past your limit. เดินไป is walk on, ช้าไป (cháa bpai) is too slow, and the word in front has already told you which.
Now the part where learners freeze, which is stacking. The full shape is verb, then path, then ไป or มา, and the slots go in that order every time: what you did, which way the movement went, and where that leaves it relative to you. เดินขึ้นไปชั้นสามครับ (doen khêun bpai chán sǎam khráp) is walk up to the third floor, away from where I am. ยกขึ้นมาหน่อยได้ไหมครับ (yók khêun maa nàwy dâi mǎi khráp) is lift it up here to me. กัดลงไปเลยนะคะ (gàt long bpai loei ná khá) is what the dentist says for bite down, where ลงไป taken as one unit supplies a closing movement rather than a clench. The last slot is almost always ไป or มา because it is the outermost layer: ขึ้น, ลง, เข้า and ออก describe the shape of the movement in the world, and ไป or มา then fixes that whole movement against the only reference point Thai cares about, the person speaking. Three slots is as far as you normally need to go. One other word competes for that tail: ไว้ (wái), leave it in that state, as in ฝากไว้ที่ป้อมยาม (fàak wái thîi bpâwm-yaam), leave it at the guard box, and กัดไว้แน่นๆ (gàt wái nâen-nâen), keep biting down. ไว้ says the result stays put; ไป and มา say where it went.
The same last slot attaches to route instructions, which is why direction words turn up in answers that contain no verb of your own at all. ตรงไป (dtrong bpai) is carry straight on, ร้านอยู่เลยธนาคารไปนิดหนึ่ง (ráan yùu loei thá-naa-khaan bpai nít nèung) is the shop is a little past the bank, ต้องอ้อมไป (dtâwng âwm bpai) is you have to go round, and ย้อนกลับไปหน่อย (yáwn glàp bpai nàwy) is go back a bit the way you came. Every one of them carries ไป, because every one describes movement away from where you and the person answering are standing together. Note that ไป rides on the verb phrase rather than on the end of the sentence, so a measure or a softener can follow it, which is what นิดหนึ่ง and หน่อย are doing in those two. Hear a direction answer carry มา instead and something has shifted: the speaker is describing your approach to a place he is picturing himself at.
One collision to keep clean. The lesson on past, future and already teaches a มา that sits behind the verb and runs an event up to the present: อยู่เมืองไทยมาห้าปีแล้วครับ (yùu meuang-thai maa hâa bpii láew khráp), I have been in Thailand five years, and ไปตลาดมา (bpai dtà-làat maa), I have just been to the market. Thai does not separate the two, and you do not need to either. What follows settles it: a stretch of time after มา makes it the time marker, and a verb of movement in front of it with no duration behind it makes it the direction. ไปตลาดมา sits honestly in both, which is exactly why it means went and came back.
The habit to build is small and mechanical. Before you say any verb that involves something moving, and that includes a message, a photograph, a parcel, a person and a price, ask where you are standing and whether the thing ends up nearer you or further away, then put ไป or มา on the end. It will feel like an extra word for a while. After that, sentences without it start to sound the way a sentence sounds with the tone left off, understandable and unfinished, which is how yours sound to a Thai ear now.