[ث] vs. [ذ] vs. [ظ]

As regards the ث, it is a straightforward sound as it resembles the English th in ‘through’ and ‘thin’. Likewise, ذ resembles the English th in ‘this’ and ‘there’. Generally, the difficulty among these three concerns ظ. Looking at the diagram, you can see that these letters are adjacent as to their place of articulation. Therefore, they are similar except for one or two pronunciation features. ظ is similar to ذ, but is it emphatic. More specifically, we raise the the root / back of the tongue when we pronounce it. Hence, ذ is non-emphatic, while ظ is emphatic. The following examples may help become aware of the difference.

[ت] vs. [د] vs. [ط]

With regard to the ت, it is similar to the English t in ‘tea’ and ‘plate’. The difference between ت and د lies in voicing. While ت is voiceless (i.e. produced without vibration in the throat), د is voiced (i.e. produced with vibration in the throat). Likewise, ط and د are similar, except that ط is emphatic. In producing the ط, we raise the tongue root. By saying the following words out loud and repeatedly, you can feel the difference between them.

[ك] vs. [ق]

On the other hand, ق and ك do not cause any difficulty for most learners. They are respectively pronounced like the English g in ‘game, and ‘go’ and k in ‘cat’ and ‘book’. Basically, most Arabs nowadays pronounce them in this manner. However, the formal (and classical) ق is lower than the ك in the mouth. When we produced it, the uvula (i.e. the hanging piece of flesh at the back of mouth and above the throat) blocks the air passage and the throat raises a bit. This pronunciation is particularly important while reading the Holy Quran. Here are minimal pair examples for practice.

[خ] vs. [غ]

By contrast, غ and خ are by far the most difficult for many learners, especially native speakers of English. Compared to English, they are closest to g and k, respectively. For example, غُبَار ‘dust’ is pronounced by an English speaker as قُبَار, and خَالِد ‘Khalid’ is pronounced as كَالِد. Looking at the diagram above, we pronounce them from the upper part of the throat. As regards the difference between them, غ is voiced (accompanied by vibration in the vocal cords) and خ is voiceless (not accompanied by vibration in the vocal cords). The best way to get these sounds right is to practice saying amply. Here is a list to begin with.

[ع] vs. [أ]

What's more, ع is another very difficult letter for most learners of Arabic. Because it close to أ in the area of articulation (as you can see in the diagram), many learners of Arabic pronounce it as أ. Relative to English, أ is similar to the glottal stop in English, that is the ‘t’ in ‘water’ and ‘butter’ in North American English. Here is how we should pronounce  ع. If you Repeat the following examples and similar example loudly and over and over again, you will comprehend the difference between the two.

[هـ] vs. [ح]

Finally, let us look at the هـ and ح, which we produce from the same area of articulation—the throat. Although they are both voiceless, ح is higher in the throat. So, it has a slightly different sound. هـ is similar to the English h in ‘hat’ and ‘hot. Because it has no English counterpart, most learners of Arabic pronounce the ح as هـ, which lead to misunderstanding and communication problems. Here is how it should be pronounced ح. Repeated practice is the best way to get the distinction between them. The following list gives you a good start.